Polymeric Nanocomposite Membranes with Phosphorene Based Pore Fillers for Fouling Control

University of Kentucky UKnowledge

Theses and Dissertations--Chemical and Materials Engineering Chemical and Materials Engineering

2020

POLYMERIC NANOCOMPOSITE MEMBRANES WITH PHOSPHORENE BASED PORE FILLERS FOR FOULING CONTROL

Joyner Eke University of Kentucky, [email protected] Author ORCID Identifier: https://orcid.org/0000-0003-0716-5070 Digital Object Identifier: https://doi.org/10.13023/etd.2020.471

Right click to open a feedback form in a new tab to let us know how this document benefits ou.y

Recommended Citation Eke, Joyner, "POLYMERIC NANOCOMPOSITE MEMBRANES WITH PHOSPHORENE BASED PORE FILLERS FOR FOULING CONTROL" (2020). Theses and Dissertations--Chemical and Materials Engineering. 127. https://uknowledge.uky.edu/cme_etds/127

This Doctoral Dissertation is brought to you for free and open access by the Chemical and Materials Engineering at UKnowledge. It has been accepted for inclusion in Theses and Dissertations--Chemical and Materials Engineering by an authorized administrator of UKnowledge. For more information, please contact [email protected]. STUDENT AGREEMENT:

I represent that my thesis or dissertation and abstract are my original work. Proper attribution has been given to all outside sources. I understand that I am solely responsible for obtaining any needed copyright permissions. I have obtained needed written permission statement(s) from the owner(s) of each third-party copyrighted matter to be included in my work, allowing electronic distribution (if such use is not permitted by the fair use doctrine) which will be submitted to UKnowledge as Additional File.

I hereby grant to The University of Kentucky and its agents the irrevocable, non-exclusive, and royalty-free license to archive and make accessible my work in whole or in part in all forms of media, now or hereafter known. I agree that the document mentioned above may be made available immediately for worldwide access unless an embargo applies.

I retain all other ownership rights to the copyright of my work. I also retain the right to use in future works (such as articles or books) all or part of my work. I understand that I am free to register the copyright to my work.

REVIEW, APPROVAL AND ACCEPTANCE

The document mentioned above has been reviewed and accepted by the student’s advisor, on behalf of the advisory committee, and by the Director of Graduate Studies (DGS), on behalf of the program; we verify that this is the final, approved version of the student’s thesis including all changes required by the advisory committee. The undersigned agree to abide by the statements above.

Joyner Eke, Student

Dr. Isabel Escobar, Major Professor

Dr. Stephen Rankin, Director of Graduate Studies

POLYMERIC NANOCOMPOSITE MEMBRANES WITH PHOSPHORENE BASED PORE FILLERS FOR FOULING CONTROL

______

DISSERTATION ______A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Engineering at the University of Kentucky

By Joyner Eke Lexington, Kentucky Director: Dr. Isabel Escobar, Professor of Chemical and Materials Engineering Lexington, Kentucky 2020

ABSTRACT OF DISSERTATION

POLYMERIC NANOCOMPOSITE MEMBRANES WITH PHOSPHORENE BASED PORE FILLERS FOR FOULING CONTROL

ABSTRACT Phosphorene is a two-dimensional material exfoliated from bulk phosphorus. Specifically, relevant to the field of membrane science, the band gap of phosphorene provides it with potential photocatalytic properties, which could be explored in making reactive membranes able to control the accumulation of compounds on the surface during filtration, or fouling. Another reason phosphorene is a promising candidate as a membrane material additive is due to its catalytic properties which can potentially destroy foulants on the membrane surface. The first goal of this study was to develop an innovative and robust membrane able to control and reverse fouling with minimal changes in membrane performance. To this end, for proof of concept, membranes were embedded with phosphorene. Membrane modification was verified by the presence of phosphorus on membranes, along with changes in surface charge, average pore size, and hydrophobicity. After modification, phosphorene-modified membranes were used to filter methylene blue (MB) under intermittent ultraviolet light irradiation. Phosphorene-modified and unmodified membranes displayed similar rejection of MB; however, after reverse-flow filtration was performed to mimic pure water cleaning, the average recovered flux of phosphorene- modified membranes was four times higher than that of unmodified membranes. Furthermore, coverage of MB on phosphorene membranes after reverse-flow filtration was four times lower than that of unmodified membranes, which supported the hypothesis that phosphorene membranes operated under intermittent ultraviolet irradiation became self- cleaning. Once it was determined that a successful synthesis of a phosphorene-modified membrane was possible, the next goal was to characterize structural and morphological changes arising from the addition of phosphorene to polymeric membranes. Here, phosphorene was physically incorporated into a blend of polysulfone (PSf) and sulfonated poly ether ether ketone (SPEEK) dope solution. Protein and dye rejection studies were carried out to determine the permeability and selectivity of the membranes. Since loss of material additive during filtration processes is a challenge, the stability of phosphorene nanoparticles in different environments was also examined. Furthermore, given that phosphorene is a new material, toxicity studies with a model nematode, Caenorhabditis elegans, were carried out to provide insight into the biocompatibility and safety of phosphorene. Results showed that membranes modified with phosphorene displayed a higher protein rejection but lower flux values. Phosphorene also led to a 70% reduction in dye fouling after filtration. Additionally, data showed that phosphorene loss was negligible within the membrane matrix irrespective of the pH environment. Phosphorene caused toxicity to nematodes in a free form, while no toxicity was observed for membrane permeates.

After gaining an understanding of the membrane characteristics, phosphorene’s ability to degrade contaminants was investigated. Nanomaterials with tunable properties show promise because of their size-dependent electronic structure and controllable physical properties. The purpose of this portion of the research was to develop and validate environmentally safe nanomaterial-based approaches for treatment of drinking water including degradation of per- and polyfluorinated chemicals (PFAS). PFAS are surfactant chemicals with broad uses that are now recognized as being a significant risk to human health. They are commonly used in household and industrial products. They are extremely persistent in the environment because they possess both hydrophobic fluorine-saturated carbon chains and hydrophilic functional groups, along with being oleophobic. Traditional drinking water treatment technologies are usually ineffective for the removal of PFAS from contaminated waters because they are normally present in exiguous concentrations and have unique properties that make them persistent. Therefore, there is a critical need for safe and efficient remediation methods for PFAS, particularly in drinking water. The proposed novel approach has also a potential application for decreasing PFAS background levels in analytical systems. In this study, a 99% rejection of perfluorooctanoic acid (PFOA) was attained alongside a 99% removal from the PFOA that accumulated on surface of the membrane. This was achieved using nanocomposite membranes made of sulfonated poly ether ether ketone (SPEEK) with two-dimensional phosphorene with pore sizes smaller than the size of PFOA. To then remove the PFOA that accumulated on the surface to foul the membranes, these were exposed to ultraviolet (UV) photolysis and liquid aerobic oxidation. The last portion of this study investigated the biocidal properties of SPEEK and phosphorene membranes under an alternating electrical potential. SPEEK and phosphorene-based membranes were synthesized and analyzed using cross-flow filtration to determine their biocidal properties. Serratia marcescens was the model bacteria and filtration was performed under alternating positive and negative voltage bias conditions. The biofouled membranes were examined for bacteria growth after three days. In the case of the SPEEK membrane, without voltage, the biofilm covered approximately 60% of the membrane surface, and under voltage, that decreased to 44%. On the other hand, the presence of an alternating voltage did not impact the microbial surface coverage on the phosphorene membranes. It is proposed that because phosphorene membranes were more hydrophobic and less charged as compared to SPEEK membranes, microbial growth adhered more strongly to the phosphorene membranes. Therefore, the alternating voltage was not effective in desorbing the strongly adsorbed biofilm layer from the phosphorene membranes. On the other hand, the employment of an alternating current on the more hydrophilic and more negatively charged SPEEK membranes was more effective at desorbing some of the attached biofilm from the membrane surface. For the first time, nanocomposite membranes were fabricated using phosphorene. This opens the field to a new class of potentially reactive membranes, or at the least, easier to clean membranes. Due to phosphorene’s properties, these membranes have the potential to be used for multiple purposes, such as compound destruction and self-cleaning membranes etc. Membrane separations of the future will not favor static membranes, i.e., membranes that only serve the function of rejecting compounds, since accumulated and potentially hazardous compounds on the surface will be released on backwash/cleaning water to make that hazardous and make the membranes hazardous at the time of disposal. Hence, dynamic

self-cleaning membranes that can simultaneously remove compounds and destroy them provide the field with an alternative.

KEYWORDS: [Nanofiltration membranes, Phosphorene, Perfluorinated Compounds, Fouling Control, Water Treatment]

Joyner Eke (Name of Student)

[09/15/2020] Date

POLYMERIC NANOCOMPOSITE MEMBRANES WITH PHOSPHORENE BASED PORE FILLERS FOR FOULING CONTROL

By Joyner Eke

Dr Isabel. C. Escobar Director of Dissertation

Dr Stephen Rankin Director of Graduate Studies

9/15/2020 Date

DEDICATION

To God the giver of life. To Rita Chinomso Eke

ACKNOWLEDGMENTS

The choice of research advisor goes a long way in the actualization of a doctorate degree.

I was very fortunate to be advised by Dr. Isabel Escobar. She is the complete package, knowledgeable mentor, and compassionate mother. Her academic and research prowess are second to none. Her directions and guidance have gone a long way in shaping my attitude to research and life. Her contributions to this academic work, loving trust, unflinching support, encouragement, critique, and advice to bring the best out of me are very appreciated. She will always have a special spot in my heart.

My ambitions towards a doctorate degree started with a meeting with Dr. Dibakar

Bhattacharyya ( Dr D.B). Thank you for the motivating speeches, the career discussions and most especially the academic guidance. I am very grateful.

I met Dr. Gail Brion at the start of my program, and we have developed a unique bond. I am grateful for all the guidance in the microbial part of my dissertation and academic contributions. Most especially I am very grateful for the warmth and love shown to me

by Lee and Dr. Brion. I am not adventurous with food, but they opened my taste buds to

delicious Mexican dishes, and I am now hooked. Thank you, Lee, for your contributions

to the electrical part of my studies.

I would like to acknowledge the contributions of Dr. Doo Young Kim to the chemistry

part of my studies. Dr. Douglas Strachan and his group contributed to my training on the

exfoliation of black phosphorus. I would like to acknowledge the contributions of Dr.

Zach Hilt, your helpful insights during my qualifiers helped shape the course of this

project. I am grateful.

iii

I would like to acknowledge the technical efforts of Nick Cprek, John May, Tricia

Coakley, my dissertation would not be complete without your valuable contributions. The

administrative staff in the department of Chemical and Materials Engineering, I am very

grateful for all the help.

I would like to acknowledge my research colleagues and lab mates, Dr. Xiaobo Dong, Dr.

Priyesh Wagh, Dr. Sneha Chede, Conor Sprick, David Lu, Dr. Saiful Islam, Dr. Ashish

Aher, Dr. Hongyi Wan, Dr. Sebastian Hernandez, Francisco Leniz, Dr. Yuxia Ji, Rollie

Mills, Dr. Anthony Saad, you made the five years in the lab fun and I am grateful for all the help provided towards the success of my degree.

The past five years have been very wonderful partly because of the numerous undergraduate students I had the pleasure to work with. Starting off with Sarah Kintner, I am grateful for the listening ears, love, and warmth you have shown me during my stay in Kentucky. You are Jannah’s cool buddy! I also acknowledge your efforts in the synthesis of some polymers used during this study. Katie Elder, I acknowledge your contributions towards developing a self-cleaning membrane, Lilian Banks, I acknowledge your contributions towards the contaminant removal project, Aissatou Diop, I acknowledge your contributions with the bacterial study, Dumebi Okoisama, I acknowledge your contributions in the polymer development project, Jacob Page, thanks for your help with the contaminant removal project, Nargiza Nigmatova, Laura Brady,

Zachary Baker and all the undergraduates that participated in one project or the other, I am very grateful for all the effort put into this study.

My life changed for the better the day I met you, Dr. Ahmed Sodiq, my husband. Your unflinching support, love, and genuine care for me is unsurpassed. I would not have had

the stamina to finish this study without your support. Thank you for being my number one

cheerleader. Thank you so much for all that you do for me. I am very grateful

My daughter, Jannah, you came into my life unexpectedly and transformed my world.

Thank you for the laughs and giggles after I have had a stressful day in the lab. I am very grateful for your unreserved love towards me.

To my parents, your discipline , guidance, and love have shaped me into the woman that

I am today. I am grateful for all of it. To my late siblings, Rita, Prisca, and Ernest, I lost

two of you during my doctorate degree and I could have given up, but because of the

unflinching support and love shown towards me when you were alive, I pushed on. To

my other siblings, Judith, Sandra, Chuks and Uche, your love and support towards me has

not gone unnoticed. I am grateful.

To my best friend Rukkayya Dabana, you have always provided a shoulder to lean on for

over 20 years, I am very grateful for that shoulder and most especially, your love and

unwavering support towards all things that concern me

TABLE OF CONTENTS ACKNOWLEDGMENTS ...... iii LIST OF TABLES ...... x LIST OF FIGURES ...... xi CHAPTER 1. Introduction and Literature Review ...... 1 1. Introduction and literature review ...... 1 1.1. Phosphorene ...... 1 1.1.1. Phosphorene Exfoliation ...... 3 1.2. Membranes for water treatment ...... 5 1.2.1. Fouling ...... 7 1.2.2. Membrane Materials ...... 16 1.2.2.1. Polysulfone (PSf) ...... 17 1.2.2.2. Polyetheretherketone (PEEK) ...... 18 1.2.3. Techniques for surface locating nanomaterials on membranes ...... 19 1.2.3.1. Self-Assembly ...... 20 1.2.3.2. Layer by Layer Assembly ...... 22 1.2.3.3. Physical and Chemical deposition ...... 25 1.2.3.4. Chemical grafting ...... 28 1.2.3.5. Other methods for fabrication of surface located nanocomposite membranes ...... 29 1.3. Per- and polyfluorinated chemicals (PFAS) ...... 31 CHAPTER 2. Research Objectives ...... 35 2.1. Hypotheses ...... 35 CHAPTER 3. Materials and Experimental ...... 39 3. Methodology ...... 39 3.1. Materials ...... 39 3.2. Preparation of phosphorene from black phosphorus...... 39 3.3. Preparation of sulfonated PEEK...... 40 3.4. Determination of Degree of Sulfonation ...... 41 3.5. Membrane preparation ...... 42 3.6. Membrane Characterization ...... 43 3.6.1. Flux Analysis ...... 43 3.6.2. Contact angle measurement ...... 44 3.6.3. Zeta potential ...... 44

3.6.4. Raman Studies ...... 45 3.6.5. Liquid-Liquid Porometer studies ...... 46 3.6.6. Morphological characterization ...... 47 3.6.7. Fourier-Transform Infrared Spectroscopy (FTIR) ...... 47 3.6.8. Transmission Electron Microscopy (TEM) and HAADF-STEM ...... 48 3.6.9. Optical Profilometer ...... 48 3.6.10. Surface roughness characterization ...... 49 3.6.11. Surface Fluorescence Characterization ...... 50 3.7. Leaching Studies ...... 50 3.8. Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) Study ...... 51 3.9. Toxicity Testing ...... 52 3.10. Biofouling Studies ...... 53 3.11. Ultra Performance Liquid Chromatography- Mass Spectrometry (UPLC-MS) ...... 55 CHAPTER 4. Self-Cleaning Nanocomposite Membranes with Phosphorene-Based Pore Fillers for Water Treatment ...... 57 4.1. Introduction ...... 57 4.2. Experimental ...... 60 4.2.1. Materials ...... 60 4.2.2. Exfoliation of Phosphorene from Black Phosphorus ...... 60 4.2.3. Membrane Preparation ...... 61 4.2.4. Flux Analysis ...... 62 4.2.5. Filtration Experimental Setup ...... 63 4.2.6. Contact Angle Measurement ...... 63 4.2.7. Zeta Potential ...... 64 4.2.8. Raman Studies ...... 64 4.2.9. Liquid–Liquid Porometer Studies ...... 65 4.2.10. Morphological Characterization ...... 65 4.2.11. Surface Fluorescence Characterization ...... 66 4.3. Results and Discussion ...... 66 4.4 Conclusions ...... 75 CHAPTER 5. Nanohybrid Membrane Synthesis with Phosphorene Nanoparticles: a Study of the Addition, Stability and Toxicity ...... 77 5.1. Introduction ...... 77 5.2. Materials and Methods ...... 82 5.2.1. Materials ...... 82

vii

5.2.2. Sulfonation of PEEK and Determination of Degree of Sulfonation ...... 83 5.2.3. Fourier-Transform Infrared Spectroscopy (FTIR) ...... 84 5.2.4. Exfoliation of Bulk Black Phosphorus ...... 85 5.2.5. Transmission Electron Microscopy (TEM) and HAADF-STEM ...... 85 5.2.6. Optical Profilometer ...... 86 5.2.7. Electrokinetic Potential Measurement ...... 87 5.2.8. Contact Angle Measurement ...... 87 5.2.9. Leaching Studies ...... 88 5.2.10. Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) Study ...... 88 5.2.11. Morphological Characterization of Membranes using X-ray photoelectron spectroscopy (XPS) and Scanning Electron Microscope (SEM) ...... 89 5.2.12. Membrane Synthesis ...... 90 5.2.13. Flux Analysis ...... 91 5.2.14. Toxicity Testing ...... 92 5.3. Results and Discussions ...... 94 5.3.1. Degree of Sulfonation and Membrane Fabrication ...... 94 5.3.2. Structural Membrane Polymer Evolution ...... 95 5.3.3. TEM Analysis ...... 97 5.3.4. Morphological Characterization of Membranes ...... 99 5.3.5. Phosphorene Leaching ...... 101 5.3.7. Phosphorene Distribution on the Membrane ...... 104 5.3.8. Flux Discussion ...... 105 5.3.9. Operational Performance of Phosphorene Membranes ...... 107 5.3.10. Toxicity of Phosphorene ...... 108 5.4 Conclusions ...... 110 CHAPTER 6. Dual Functional Phosphorene Nanocomposite Membranes for the Treatment of Perfluorinated Water ...... 113 6.1. Introduction ...... 113 6.2. Materials and Methods ...... 118 6.2.1. Materials ...... 118 6.2.2. Preparation of phosphorene ...... 119 6.2.3. Sulfonation of poly ether ether ketone ...... 119 6.2.4. Water Flux Analysis ...... 119 6.2.5. Determination of the water interaction parameter of the membranes ...... 120 6.2.6. Treatment Processes ...... 120

viii

6.2.7. Membrane fouling analysis ...... 121 6.2.8. Structural and profile studies with Scanning Electron Microscope (SEM) and X-ray photoelectron spectroscopy (XPS) ...... 124 6.2.9. Surface roughness characterization ...... 125 6.3. Results and Discussion ...... 125 6.3.1. PFOA Filtration Studies ...... 125 6.3.2. Hydrophobicity ...... 128 6.3.3. Fouled PFOA Removal ...... 129 6.3.4. Membrane Morphology ...... 131 6.4. Conclusions ...... 138 CHAPTER 7. Investigation of the Effect of an Applied Potential as a Biofouling Control Technique ...... 140 7.1. Introduction ...... 140 7.2. Materials and Methods ...... 141 7.2.1. Preparation of phosphorene ...... 141 7.2.3 Sulfonation of poly ether ether ketone ...... 142 7.2.4 Membrane preparation ...... 142 7.2.5 Biofouling studies ...... 143 7.3. Results and Discussion ...... 146 7.4 Conclusions ...... 150 CHAPTER 8. Conclusions and Recommendations ...... 151 8.1. Conclusions ...... 151 8.2. Recommendations ...... 154 APPENDICES ...... 157 APPENDIX 1 FILTRATION DATA ...... 157 APPENDIX 2: DYNAMIC LIGHT SCATTERING DATA ...... 163 REFERENCES ...... 205 VITA ...... 228

LIST OF TABLES Table 1: Flux values of phosphorene membranes operated under UV irradiation and without UV irradiation ...... 74 Table 2: Assignment of FTIR bands at different wavelength ...... 97 Table 3: Flux values of phosphorene membranes operated under visible and UV light sources 107 Table 4: Color difference values of the membranes ...... 148

LIST OF FIGURES Figure 1: Structure of phosphorene ...... 3 Figure 2: Diagram showing the four main membrane processes [45] ...... 7 Figure 3: Typical filtration flux diagram showing the difference between reversible and irreversible fouling effects on the flux ...... 9 Figure 4: Types of fouling ...... 10 Figure 5: Schematic representation of all the resistances in a porous membrane during filtration 12 Figure 6: Factors affecting membrane fouling: (a) foulant characteristics ; (b) membrane properties; (c) operational conditions and (d) feed water characteristics [73]...... 14 Figure 7: Structure of polysulfone ...... 18 Figure 8: Structure of polyetheretherketone...... 19 Figure 9: Perfluorooctane sulfonic acid (top image); Perfluorooctanoic acid (bottom image) ...... 32 Figure 10: Current treatment technologies for PFAS removal [167] ...... 33 Figure 11: Sulfonation of PEEK to SPEEK [183]...... 41 Figure 12: Nomenclature of aromatic protons of SPEEK ...... 42 Figure 13: Schematic of Leaching Study Setup ...... 51 Figure 14: Biofouling experimental setup ...... 55 Figure 15: Preparation of a phosphorene-incorporated nanocomposite membrane ...... 60 Figure 16: Phosphorene characteristic Raman bands ...... 67 Figure 17: Cross-section SEM analyses of (A) SPEEK membranes and (B) phosphorene- membranes with some of the phosphorene nanoparticles marked in red, and surface SEM analyses of (C) SPEEK membranes (50-micron magnification) and (D) phosphorene-membranes (10-micron magnification) before filtration ...... 68 Figure 18: A) EDX spectrum of SPEEK membrane showing the presence of carbon, oxygen, and sulfur. (B) EDX spectrum of phosphorene containing SPEEK membrane showing the presence of carbon, oxygen, sulfur, and phosphorus...... 69 Figure 19: Surface charge vs pH plot of (A) SPEEK membrane and (B) phosphorene-modified membrane...... 71 Figure 20: (A) Flux analyses of SPEEK membrane under UV irradiation at a constant pressure of 2.06 bar (B) Flux analysis of the phosphorene-modified membrane under UV irradiation at a constant pressure of 2.06 bar ...... 73 Figure 21: (A) Fluorescent image of SPEEK membrane after the reverse-flow filtration. (B) Fluorescent image of phosphorene-modified SPEEK membrane after the reverse-flow filtration...... 75 Figure 22: Fabrication of blend polymeric membrane ...... 91 Figure 23: 1H NMR spectrum of SPEEK in dimethyl sulfoxide ...... 95 Figure 24: FTIR spectra of phosphorene and SPEEK: PSf membranes over the region 400-4000 cm-1 ...... 96 Figure 25: FTIR spectra of phosphorene and SPEEK: PSf membranes over the region ...... 97 Figure 26: TEM images of 2D phosphorene in different solvents (A) NMP and (B) water ...... 98 Figure 27: (A) three dimensional and (B) bottom view of SPEEK: PSf membranes showing the surface morphology ...... 100 Figure 28: (A) three dimensional and (B) bottom view of phosphorene membranes showing the surface morphology ...... 100 Figure 29: Leaching experiment of phosphorene in membrane ...... 102 Figure 30: Cross-section images of (A) SPEEK: PSf membrane, and (B) and phosphorene membrane ...... 104

Figure 31: Depth profile scan on phosphorene membranes ...... 105 Figure 32: (A) Flux analysis of SPEEK: PSf membranes and (B) Phosphorene membranes ..... 106 Figure 33: Caenorhabditis elegans mortality in response to phosphorene exposure over 24 h in Moderately Hard Reconstituted water (MHRW). The double asterisks indicates statistical significance at p < 0.01...... 110 Figure 34: Effect of free phosphorene exposure over 24 h on reproduction in Caenorhabditis elegans in A) K-Medium and B) Moderately Hard Reconstituted Water (MHRW). The double asterisks indicates statistical significance at p < 0.01...... 110 Figure 35: Schematics of the experimental process ...... 118 Figure 36: (A) Flux results (liters/m2-hr) for the phosphorene membrane at a constant pressure of 2.06 bar, showing the initial precompaction period, where pure water was filtered through the membranes until a near-constant flux value was attained. After precompaction, the filtration of PFOA was carried out, and it was followed by reverse flow filtration to simulate backwashing. (B) Normalized flux decline...... 127 Figure 37: Water interaction parameter graph, to represent different levels of hydrophobicity, for the different membrane surface treatment techniques studied...... 129 Figure 38: Removal of PFOA from the surface of the membrane after UV irradiation for two different periods of time, and after bubbling of oxygen for three different periods of time...... 131 Figure 39: SEM images of membranes after PFOA removal procedure: (A) baseline clean membrane, (B) after PFOA filtration, (C) after UV treatment of PFOA-fouled membrane surface, and (D) after oxygen treatment of PFOA-fouled membrane surface...... 133 Figure 40: Depth atomic profile showing the percentage of fluorine on the membrane surfaces and within their pores after (A) filtration, (B) UV irradiation, and (C) oxygenation...... 135 Figure 41: AFM images of membrane surface after treatment: (A) plain/clean membrane, (B) the membrane after filtration of PFOA, (C) the membrane after filtration of PFOA and irradiation with UV, and (D) the membrane after filtration of PFOA and oxygenation...... 136 Figure 42: Possible pathways for the degradation of PFOA after (A) UV photocatalysis and (B) liquid aerobic oxidation [337]...... 137 Figure 43: Experimental set for biofouling study ...... 145 Figure 44: Images of (A) Negative control (B) Positive control ...... 146 Figure 45: Images of (A) Phosphorene membrane under no voltage and (B) phosphorene membrane under alternating potential...... 147 Figure 46: Image of (A) SPEEK membranes under no voltage and (B) SPEEK membranes under an alternating potential ...... 147 Figure 47: Surface charge of (A) SPEEK membrane and (B) phosphorene-modified membrane ...... 149

xii

CHAPTER 1. Introduction and Literature Review

1. Introduction and literature review

1.1. Phosphorene The use of nanomaterials with tunable optoelectronic properties shows promise for numerous technologies, such as photovoltaics, transistors, and light-emitting diodes [1-4]

because of their size-dependent electronic structure and controllable physical properties.

Importantly, nanomaterials have versatile morphologies, such as zero dimensional (0D)

nanoparticles, one dimensional (1D) nanowires/rods/belts, two dimensional (2D)

nanosheets/plates and three dimensional (3D) porous frameworks/networks [5]. Two

dimensional nanomaterials can be described as materials that do not require a substrate to

exist and can be isolated as freestanding one atom thick sheets [6]. They are typically

generated from bulk layered crystalline solids[7]. These solids consist of successive layers

of covalently bonded atomic layer planes ranging from one to multiple atoms thick,

separated successively by Van der Waals gaps [8]. Single monolayers are generated via a

variety of methods, primarily mechanical exfoliation, liquid exfoliation, or lithium-

intercalation/deintercalation of these layered materials [7]. The properties of these

materials are usually very different from those of their 3D counterparts [9]. The first 2D

material to be isolated was graphene, a zero-overlap semimetal. Since its discovery,

graphene has excelled in various applications in the field of membrane science and other

aspects of science and technology and gained prominence as a wonder material. But, the

symmetrical electrical band structure of graphene, i.e., its zero-band gap energy has limited

its use for many applications. The success of graphene has inspired exploration of other

2D layered materials. The family of 2D crystals has grown to include metals (e.g., NbSe2), 1

semiconductors (e.g., MoS2), and insulators (e.g., hexagonal boron nitride (hBN))[9]. The quest for a variety of high-performance devices has necessitated the search for additional layered materials that exhibit a wider operating range in their key properties, such as the electronic band gap and carrier mobility [10]. Among recently discovered 2D materials, phosphorene is one of the most intriguing due to its interesting properties and numerous foreseeable applications.

Phosphorus which constitutes about 0.1% of the Earth’s crust is one of the most abundant elements [11], and it exists as several allotropes. White and red phosphorus are the most commonly seen allotropes used typically for making explosives and safety matches [12].

Black phosphorus (BP), though rarely mentioned, is the most stable allotrope of phosphorus [13], and it combines high carrier mobility with a fundamental band gap [14].

Graphite and black phosphorus (BP) are the only known monotypic van der Waals crystals

[15, 16]. The phosphorus atoms of BP covalently bond to three neighboring atoms, but unlike graphene, BP forms a puckered structure with out of plane ridges. Unlike carbon, phosphorus has only three valance electrons which leads to BP being semiconducting since each atom is bonded to three neighboring atoms [15]. Exfoliated, p-type semiconducting

BP flakes possess mobilities of ~200-1000 cm2 /V-s at room temperature, current on/off ratios of ~104 and anisotropic transport. Consequently, BP shows promise as a nanomaterial that could complement or exceed the electronic, spintronic, and optoelectronic properties of graphene [17, 18]. Phosphorene is a single atomic layer of BP that shows semiconducting properties [19]. Figure 1 shows the structure of phosphorene.

Phosphorene distinguishes itself from other 2D layered materials by its unique structural characteristics, relatively large direct bandgap and good charge carrier mobilities [20].

Phosphorene has a thickness-dependent direct band gap that changes to 1.88 eV in a

monolayer from 0.3 eV in the bulk. The chemical, physical, optical, and electronic

properties of phosphorene depend greatly upon its morphology and structure. Although

bulk BP is the thermodynamically most stable allotrope of phosphorus under ambient

conditions, it has a major drawback. However, single- or multi-layer phosphorene made

from bulk BP is not stable under ambient conditions because of its highly hygroscopic

nature; that is, it absorbs moisture from the air [21]. However, recent work has shown that

the technique used to exfoliate phosphorene from BP can impact the stability of phosphorene. Basic liquid exfoliation has been shown to produce stable phosphorene [22].

Figure 1: Structure of phosphorene

1.1.1. Phosphorene Exfoliation

Reliable production of atomically thin, single, or layered phosphorene with uniform size

and properties from bulk BP is necessary for incorporation into experimental procedures

and for use in device fabrication. The three major techniques for exfoliating phosphorene

are by mechanical exfoliation, liquid exfoliation, and plasma-assisted fabrication.

In mechanical exfoliation, one important precondition is that the interlayer interaction in

the bulk counterpart is dominated by weak vdWs forces, making possible the cleavage of

the materials using just an adhesive tape [10]. BP consists of layered structures held

together by weak interlayer forces with a significant vdWs character, this suggests that

few-phosphorene can be obtained by this exfoliation method [10]. This process involves

the use of a scotch tape to peel thin flakes from bulk crystal onto doped silicon wafer

covered with a layer of thermally grown silicon dioxide [23]. Although, this technique

produces single-crystal flakes of high purity that are suitable for fundamental

characterization, however, this method is not scalable and there is a lack of systematic

control of flake thickness and size [14, 24-26].

Another approach used to fabricate monolayer phosphorene is by the combination of

mechanical cleavage and plasma thinning, called plasma-assisted fabrication [27]. With

this technique, thin phosphorene films are first exfoliated onto SiO2/Si substrate by

mechanical exfoliation, and after Ar+ plasma treatment, monolayer phosphorene is obtained. This method provides an improved way for controlling the thickness of phosphorene, but the requirement for laser scanning makes it challenging for scale-up applications [10, 27].

Lastly, liquid exfoliation has been explored for syntheses of two-dimensional materials

[28-30]. This technique involves immersion of the bulk solid into a liquid, typically N- methyl-2-pyrrolidone (NMP), and the two-dimensional materials are ultrasonically exfoliated [31]. The physical basis for the exfoliation relies on an energy match between the solvent and the surface of the two-dimensional material in question balancing the energy required for exfoliation [32]. Interestingly, the degradation for phosphorene 4

obtained by liquid-phase exfoliation occurs more slowly than that for phosphorene

prepared by mechanical cleavage, suggesting that solvent exfoliation is a more efficient

method producing more stable phosphorene nanoflakes [33, 34]. Choosing the right solvent

is an important step to obtain high quality phosphorene nanosheets. Recently, several

studies investigated and compared the effect of different solvents on the stability of

phosphorene [22, 34, 35]. Among many types of solvents, N-methyl-2-pyrrolidone (NMP)

and N-cyclohexyl-2-pyrrolidone (CHP) were found to provide stable and high yield

phosphorene dispersions [36].

Since stable phosphorene can now be synthesized, this opens a new field of research that

can explore its properties. Phosphorene can be used to synthesize heterostructures with other compounds, it can be used in making catalysts, batteries, and supercapacitors.

1.2. Membranes for water treatment

The scarcity of clean water is a growing challenge because of rapid population growth, extended droughts and increased human demands. Membranes are favored over many other

technologies for water treatment because, in principle, they require no chemical additives,

can be performed isothermally at low temperatures, and they do not require regeneration

of spent media [37]. Also, upscaling and downscaling of membrane processes as well as

their integration into other separation or reaction processes are relatively easy [38].

Membrane processes are increasingly used for removal of bacteria, microorganisms,

particulates and natural organic material, which can impart color, tastes, and odors to water

and react with disinfectants to form disinfection byproducts [39]. Membrane separation

techniques are commonly grouped under four headings based on the driving force behind

the operation. They include pressure-driven processes (microfiltration, ultrafiltration,

nanofiltration and reverse osmosis), concentration-driven processes (dialysis,

pervaporation, forward osmosis and gas separation), electric potential gradient driven

processes (electrodialysis, membrane electrolysis, electrodeionization and electrofiltration)

and thermal-driven processes (membrane distillation). Among the different membrane

separations, pressure-driven processes are the simplest in terms of their ability to separate

particulates in liquid and gas feed streams according to size [40]. By utilizing pressure as

the driving force for separation and with a membrane acting as a semipermeable barrier,

pressure-driven processes produce a higher flux compared to their thermal and

concentration-based separation counterparts. Types of pressure-driven membrane

separation techniques are categorized according to membrane pore size, which, in turn,

dictates the degree of separation achieved. These categories are microfiltration (MF) 0.03

to 10 microns, ultrafiltration (UF) 0.002 to 0.1 microns, nanofiltration (NF) 0.001 microns,

and reverse osmosis (RO), which is non-porous. Figure 2 shows the types of materials that can be separated using these membrane processes. The main factors that determines the durability of membranes and permeate fluxes in cross-flow pressure-driven membrane separation processes are the phenomena of concentration–polarization (i.e., accumulation of rejected species at the membrane surface) and fouling (e.g., solute and microbial adhesion) on the membrane surface [41].

NF membranes have been largely developed and commercialized over the past decade because they show promise for the separation of neutral and charged solutes in aqueous solutions, offer low operation pressure, high flux, and low operation and maintenance costs

[42]. Two important NF features include having a molecular weight cut-off (MWCO)

between that of RO and UF, which ranges from 200 to 2000 Da, and the ability to separate

electrolytes [43]. NF membranes typically have a high retention for multivalent ions and a moderate retention for monovalent ions, which is due to sieving, electrostatic interactions between the membrane and the ions or between the ions themselves, and differences in diffusivity or solubility [44].

Figure 2: Diagram showing the four main membrane processes [45]

1.2.1. Fouling Membrane separation processes are in high demand because of their superior separation performance; however, a rapid drop of the permeate flux over time due to the accumulation

of rejected materials on the membrane surface, known as membrane fouling, has limited

the adaptation of membrane-based operations. Fouling in pressure driven membrane

processes can be described as the accumulation of suspended/dissolved substances on the

external surface or within the pores of the membrane and at the pore walls[46]. It leads to

a reduction in the membrane performance, decline of the membrane lifespan and,

ultimately, increase in the operation costs. Membrane fouling can be grouped under two 7

broad headings, reversible fouling, and irreversible fouling. Reversible fouling can be

described as the loosely attached fouling element that can be removed by physical

techniques such as relaxation and back-washing[47]. On the other hand, irreversible

fouling results from strong attachment of foulants on the membrane which can only be

removed by chemical means and in some cases, permanent damage occurs to the

membrane.

This concept can be described graphically as seen in Figure 3. There are three stages during

a typical filtration process, the precompaction stage with pure water (region 1), the

filtration stage with feed solution (region 2) then lastly the reverse flow filtration stage with pure water (region 3). The membrane flux in region 1 is largely controlled by pore size and applied pressure (Darcy’s law)[48]. In Region 2, the flux Jt, declines over time during

the filtration process because of membrane fouling. The reverse flow filtration stage, region

3, is a physical cleaning step and a flux increase is observed (from J1 to J2) due to reversible

fouling. In contrast, the decline from J0 to J2 is due to irreversible fouling because despite

the cleaning procedure, the flux Jt could not return to Jo because of fouling.

Figure 3: Typical filtration flux diagram showing the difference between reversible and irreversible fouling effects on the flux Based on the type of foulant, fouling can be divided into colloidal, organic, inorganic, and biological fouling. Figure 4 provides a summary of the four major kinds of fouling and shows their interdependency on one another. Colloidal fouling leads to pore clogging and cake formation. Backwashing (reverse flow filtration) is an effective way to partially recover the membrane performance[49]. Backwashing pushes colloidal particles from the pore structure into the feed solution, where they are removed by crossflow filtration [50].

Colloids are fine particles whose characteristic size fall within the size range of 1–1000 nm.

In pressure-driven membrane systems, these fine particles have a strong tendency to foul the membranes, causing a significant loss in water permeability[51]. Colloidal fouling is influenced by many factors such as the colloids size, shape, charge as well as interactions with ions of the colloids[52]

Figure 4: Types of fouling Organic fouling is caused by organic compounds present in water, which usually consist

of humic substances and organic acids[53]. Natural organic matter (NOM) is a major

foulant of membranes used in water treatment [54, 55]. NOM is comprised of a wide range

of hydrophilic and hydrophobic components [56]. The hydrophobic fractions are mainly humic and fulvic acids that are metabolized by natural or biological degradation, with aromatic carbon and carboxyl groups making up their structures [57-59]. The hydrophilic fraction stems from hydrophilic polysaccharides and proteins, that have aliphatic carbons and hydroxyl groups [60]. Researchers have reported the hydrophobic fraction as the major foulant during surface water filtration [61-63] since it possesses higher aromaticity properties and greater adsorptive tendencies due to hydrophobic interactions [64]. The hydrophilic NOM fraction makes lower contributions to organic matter fouling compared to the hydrophobic fraction [60, 65].

Biofouling is the process of microorganism adhesion and proliferation on membranes; it is the formation of biofilm to an unacceptable degree that increases operational costs[66]. For

a biofilm to form, a source of nutrient and the microorganism that depends on the nutrient

must be present. Prevention of biofouling involves (i) reducing the concentration of

microorganisms and/or reducing the concentration of nutrients by pretreatment, and/or (ii)

performing preventive/ curative cleanings. A number of studies [67-69] have identified some trends with respect to short-term cell adhesion and biofilm growth with controlled bacterial strains. Generally, surface roughness and hydrophobicity are key predictors of cell adhesion with neutral, smooth hydrophilic surfaces having the lowest propensity to biofouling[68].

Inorganic fouling is the broad term used to describe precipitation and/or particulate fouling.

Precipitation fouling arises from a supersaturated solution, ionic species in the solution are transported by diffusion to the membrane surface thus leading to the crystallization of insoluble species. Particulate fouling in contrast, arises from the diffusion of colloidal matter to the surface of the membrane[70]. In general, inorganic fouling is caused by a high concentration of inorganic salts in the feed water. Presence of alkaline earth metal cations

,such as ,magnesium (Mg2+) and calcium (Ca2+) ions, in combination with polyanions, like,

3− 2− 2− phosphate (PO4 ) , sulphate (SO4 ), and carbonate (CO3 ) ions often leads to the

formation of inorganic scaling on the membrane surface[71] but this tends to be an

insignificant issue.

Darcy’s Law is used to explain the characteristic of membrane fouling as shown in (Eq.

1) below [72];

= /( ) (1)

𝐽𝐽 ∆𝑃𝑃𝑇𝑇 𝜇𝜇 ∙ 𝑅𝑅𝑡𝑡 represents permeate flux, represents transmembrane pressure, represents total

𝑇𝑇 𝑡𝑡 resistance𝐽𝐽 of the membrane ∆and𝑃𝑃 µ represents permeate viscosity. The𝑅𝑅 total resistance of

the membrane ( ), which is the sum of all other resistance responsible for decrease in

𝑡𝑡 permeate flux, is𝑅𝑅 given in (Eq. 2).

= + + + (2)

𝑅𝑅𝑡𝑡 𝑅𝑅𝑚𝑚 𝑅𝑅𝑐𝑐𝑐𝑐 𝑅𝑅𝑐𝑐 𝑅𝑅𝑝𝑝 Where represents the intrinsic membrane resistance, represents the resistance due

𝑚𝑚 𝑐𝑐𝑐𝑐 to concentr𝑅𝑅 ation polarization, represents cake resistance𝑅𝑅 and represents pore

𝑐𝑐 𝑝𝑝 blocking resistance. Figure 5 i𝑅𝑅s a good representation of the position𝑅𝑅 of each resistance in membrane fouling.

Figure 5: Schematic representation of all the resistances in a porous membrane during filtration

The type of membrane used is important to determine the type of fouling mechanism and

resistance responsible for permeate flux decrease in filtration. For example, (Eq. 3)

represents total resistance for a porous membrane, for a non-porous membrane in which

there is no pore blocking resistance, is excluded from the model equation.

𝑅𝑅𝑝𝑝 12

The type of fouling that occurs on membrane surfaces is mainly affected by the solution chemistry of the feed water, the concentration, and finally the properties of foulants present in the feed water. Operational conditions like temperature and flowrate of feed water are also important because they control the extent of fouling [73]. As seen in Figure 6, a plethora of factors influence fouling. Membrane fouling is initiated by the complex chemical and physical interactions on the surface of membrane and different fouling constituents present in the feed water. Mass transport across the membrane can lead to adsorption, accumulation and/or attachment of transporting materials onto the surface or inside the pores of the membrane. Therefore, any factors that has the capacity to change the chemical properties of feed water and hydrodynamic properties of membrane modules can effect a change in the overall performance of the membrane [74]. Hence, the combined chemical and physical effects will control the severity of the fouling as well as the degree of attachment of the foulants to the membrane and effective fouling control strategies effectively [75].

Figure 6: Factors affecting membrane fouling: (a) foulant characteristics ; (b) membrane properties; (c) operational conditions and (d) feed water characteristics [73].

The choice of fouling control depends on the type of foulants. The three common

approaches to mitigate membrane fouling include boundary layer (velocity) control,

membrane modifications, and combined (external) fields[76].

Boundary layer (velocity) control can occur because the boundary layer thickness or resistance on a surface depends on the velocity of flow on the surface. From the Prandtl’s boundary layer theory and Navier-Stokes equations, applied to flow over a flat sheet, the boundary layer thickness (δ) can be expressed as by equation 1:

δ = 4.6052ν/V (1) where ν is the kinematic viscosity of the permeate and V is the velocity of the flow across the membrane due to pressure drop [77, 78]. This equation suggests that, by increasing the velocity of flow, one can decrease the boundary layer thickness or the resistance due to the boundary layer [76]. This velocity approach was the major reason for the development of

crossflow or tangential flow membrane units that are now widely used [79]. The use of

velocity to control fouling was also the motivation for the incorporation of high agitation

in dead-end membrane units [76]. The velocity-induced turbulence helps minimize

membrane fouling by continually “sweeping” the membrane surface hence displacing the

fouling material off the surface.

Membrane modifications influence fouling control because if the membrane material can

limit the interaction between foulants and membrane surface, fouling can be minimized

[76]. Thus, the development of new membrane materials and/or surface modification is another way to address fouling. The membrane material affects important parameters that determine or control the extent of fouling such as membrane surface charge, hydrophobicity of the membrane, and surface roughness[80].

The use of external fields for fouling control addresses most limitations of the velocity and membrane modification control approaches [76]. Foulants that create fouling issues are usually negatively charged thus applying a direct electric field during filtration can hinder their attachment to the membrane surface through electrostatic repulsion for a like charged membrane or electrophoresis for an unlike charged membrane [81]. The concept behind

electro-filtration is the application of a vertical electric field that can act on charged molecules and prevent a gel layer formation on the membrane[82] by lifting the fouling particles off the membrane surface and facilitating transport through bulk flow.

Simultaneously, electroosmosis allows for more fluid to flow across the membrane[76, 83,

84]. This method is efficient and environmentally friendly because it does not create secondary pollution. It is specially efficient with hindering biofilm proliferation during

filtration by preventing the secretion of extracellular polymeric substances(EPS) which propagates biofouling [81].

1.2.2. Membrane Materials

Membranes are often made of inorganic materials, polymeric materials, or a combination of both. Organic polymeric materials are traditionally used in pressure-driven membrane processes. For MF, the most often used materials are the hydrophobic polytetrafluoroethylene (PTFE), poly (viny1idene fluoride) (PVDF), polypropylene (PP), polyethylene (PE), and hydrophilic materials include cellulose esters, polycarbonate (PC), polysulfone/poly (ether sulfone) (PSf/PES), polyimide/poly (ether imide) (PVPEI), aliphatic polyamide (PA), and polyetheretherketone (PEEK). UF membrane materials include polysulfone/poly (ether sulfone)/sulfonated polysulfone, poly (vinylidene fluoride), polyacrylonitrile and related block-copolymers, cellulosics such as cellulose acetate, polyimide/poly (ether imide), aliphatic polyamide, and polyetheretherketone.

Polymer blends, e.g., with polyvinylpyrrolidone (PVP) are commonly used to increase the hydrophilicity of these membranes. For NF, materials like aromatic polyamide, polysulfone/poly (ether sulfone)/sulfonated polysulfone, cellulose acetate, or poly(piperazine) amide are typically used [85]. Polymer blending is used to obtain new types of materials with a wide diversity of properties intermediate between those of the pure components. The blended membranes have better permselectivity and permeability than those made using individual polymers[86]. The hydrophilic–hydrophobic balance as well as other properties, such as physical structure and surface/pore charge of a membrane system can be easily altered if the membrane is prepared from multi-component polymer blends [87]. For this project, the polymer used is a blend of polysulfone (PSf) and 16

polyetheretherketone (PEEK), the solvent is N-methyl pyrrolidone (NMP) and the nonsolvent is water. [88]. Most microporous membranes are prepared by non-solvent induced phase separation (NIPS) [89], which involves preparation of a membrane solution

(known as dope), casting and phase separation. The membrane dope solution contains polymers and solvents; however, in many cases it also contains other additives with the aim to improve processing conditions and/or performance of resulting membrane [90].

1.2.2.1. Polysulfone (PSf)

Polysulfone (Figure 7) has excellent physicochemical properties such as chemical resistance, thermal stability and mechanical strength [91]. However, the hydrophobicity of

PSf often causes the adsorption and deposition of foulants (proteins, colloids, particles, etc.) on the membrane surface and within pores, which leads to decreases in permeation flux separation ability of the membrane during operation [91]. Enhancing the hydrophilicity of the polymer is assumed to yield a better performance in terms of permeability, antifouling properties and solute rejection [92] Specifically, by increasing the number of hydrogen bonding sites at the surface, the interfacial acid−base forces are maximized, thereby allowing the formation of an interfacial layer of tightly bonded water molecules that are highly oriented and have slow dynamics. The displacement of water molecules involves work that increases the free energy of the system, and this hydration layer provides a repulsive barrier against the adsorption of foulants [93]. Many studies of modification of PSf membranes have been made to enhance their hydrophilicity. These studies can be divided into three: blending with hydrophilic materials [94] or with minerals including silica and zirconium dioxide (ZrO2) [95, 96]; grafting with hydrophilic polymers,

monomers or functional groups [97-99]; and coating with hydrophilic polymers [100]. 17

Among these methods, blending with inorganic materials is very common due to convenient operations, mild conditions, and high performance [101].Figure 3 shows the chemical structure of the Polysulfone molecule.

Figure 7: Structure of polysulfone 1.2.2.2. Polyetheretherketone (PEEK) PEEK is a highly thermostable polymer with a Tg of 150 ◦C [102]. Studies have shown that PSf/SPEEK blend membranes had substantially∼ higher water flux, salt rejection, porosity, along with greatly reduced particle adhesion compared to the PSf membranes

[103-105]. PEEK is usually sulphonated to increase its hydrophilicity. Sulfonation improves membrane properties in terms of better wettability, higher water flux, higher antifouling capacity, better permeability, and increased solubility in solvents for processing

[102]. The properties of sulphonated PEEK (SPEEK) membranes are highly dependent on the degree of sulfonation (DS). SPEEK membranes with high DS exhibit high proton conductivity and ion exchange capacity value, but a large number of sulfonic acid groups also results in poor mechanical property [106]. SPEEK has been shown to provide nanofiltration membranes with high permeability and high rejection of salt properties

[107]. Figure 8 shows the chemical structure of the PEEK molecule.

Figure 8: Structure of polyetheretherketone.

1.2.3. Techniques for surface locating nanomaterials on membranes

This section has been published in the following report in a journal: Esfahani, Milad Rabbani, Sadegh Aghapour Aktij, Zoheir Dabaghian, Mostafa Dadashi Firouzjaei, Ahmad Rahimpour, Joyner Eke, Isabel C. Escobar et al. "Nanocomposite membranes for water separation and purification: Fabrication, modification, and applications. Separation and Purification Technology 213 (2019): 465-499. [108]

Mixed matrix membranes (MMMs), consisting of polymeric materials and permeable or impermeable submicron/nano-sized particles, have been extensively studied for liquid and gas separation to show enhanced selectivity, permeability, tortuosity and/or mechanical stability [109, 110]. A variety of inorganic nanoparticles such as zeolites [111], carbon nanotubes[112], alumina (Al2O3)[113], silica (SiO2) [114], zirconium dioxide (ZrO2)

[115], zinc oxide (ZnO) [116], silver[117] and titanium oxide (TiO2) [118], have been used

as additives in - formulation of different polymeric membranes [119]. For instance, coating

the membrane surface with titanium dioxide (TiO2) nanoparticles and then applying UV

radiation - results in photocatalysis, and groups of active oxidant reagents appear on the

surface of the membrane, which lead to decomposition and removal of organic membrane

foulants [120]. However, the benefits of added particles are limited by nanoparticle aggregation and their poor adhesion to the base polymeric matrix [121]. High

concentrations also often lead to poor mechanical stability in the membrane [121].

Therefore, seeking fabrication methods to incorporate nanoparticles into the membrane

matrix while avoiding these drawbacks is the focus of much research effort. Some of the

methods include self-assembly [122], layer by layer assembly [123], chemical grafting

[124], and physical [125] and chemical deposition [126] of nanoparticles on the membrane

surface

1.2.3.1. Self-Assembly

Self-assembly is a spontaneous process by which molecules and nanophase entities may

materialize into organized aggregates, networks or patterns through various interactive

mechanisms, such as electrostatics, chemistry, surface properties and via other mediating

agents [127]. Depositing nanoparticles on membrane surfaces by self-assembly is often used for incorporating nanoparticles into membrane matrixes. There are different mechanisms by which self-assembly of molecules and nanoclusters can be accomplished.

These mechanisms include electrostatic and surface forces[128], and chemical interactions

self-assembly techniques [129]. Self-assembly by electrostatic interactions is governed by

the adsorption and desorption equilibria in cationic and anionic solutions [127]. Bae et al.,

[128] prepared fouling-resistant TiO2/polymer nanocomposite membranes nanocomposite

membranes via electrostatic self-assembly between TiO2 nanoparticles and sulfonic acid

groups on the membrane surface. TiO2 nanocomposite membranes displayed a cake layer resistance of 33.27 x1011 m-1, while polymeric membrane had a cake resistance of 58.7

x1011 m-1, which indicated a decrease in membrane fouling when using the nanocomposite

membranes [128]. Likewise, an anti-fouling poly (styrene-alt-maleic anhydride)/poly

(vinylidene fluoride) (SMA/PVDF) blend membrane was prepared by the electrostatic self- 20

assembly between anatase TiO2 nanoparticles and –COOH groups on the membrane

surface [122]. The TiO2 particles were shown to tightly absorb on the surface of the

SMA/PVDF blend membrane and the amount of TiO2 nanoparticles was higher with the

increase of –COOH groups hydrolyzed from SMA in blend membranes (increased from

4.65 wt.% to 6.86 wt.%).

As a drawback, electrostatic interaction- in a self-assembly method, can result in a the lack

of orientation of functional fragments[130]. on the other hand, chemical self-assembly is far more specific in fixating functional groups, yielding robust and permanent structures.

Therefore, chemical self-assembly provides a method of achieving more stable self- assembled films [127]. Kim et al.,[129] hybridized TiO2 nanoparticles with thin-film-

composite (TFC) aromatic polyamide membranes by self-assembly through H-bond

interactions with the COOH group on the membrane surface to result in a tightly self-

assembled structure with sufficient bonding strength to support the use of the fabricated

membranes for reverse osmosis applications [129]. Jo et al.,[131] synthesized fouling

resistant membranes with high water flux and moderate loss of solute rejection by

chemically self-assembling zinc oxide (ZnO) nanoparticles onto aminated

polyethersulfone (PES-NH2) ultrafiltration membranes [131] by reacting amine groups

with thionyl chloride formed on ZnO nanoparticles. In another example, He et al.,[132]

using freestanding nanoparticle membranes of different core materials (Au, Fe/Fe3O4, and

CoO) with different core sizes (mean diameter 5, 13.8, and 8.5 nm, respectively) and

different capping ligands (dodecanethiol, oleylamine, and oleic acid, respectively),

demonstrated that a drying-mediated chemical self-assembly process could be used to

create close-packed monolayer membranes that span holes tens of micrometers in diameter

[132].

1.2.3.2. Layer by Layer Assembly

Layer by layer (LbL) assembly is a technique by which organic and inorganic

multicomponent films are built up on various substrates through complementary

interactions of the adsorbing species[133]. LbL used to create ultrathin advanced surface

coatings on a wide range of surfaces. The first layer is adsorbed based on electrostatic

interactions and thereafter the deposition is driven by means of electrostatic H-bonding, covalent and charge transfer interactions. This technique is well established in forming highly dense and compact ultrathin films from various kinds of organic or polymeric materials, with precise control of layer composition and thickness [134, 135]. LbL is an

effective strategy for fabricating functionalized multilayers on a membrane surface, and

since no adverse chemical reactions take place during the procedure, the properties of the

original membrane are not altered by this multiple film loading modification[136].

Complementary interactions of the LbL assembly typically can be driven by electrostatic

interactions [137], hydrogen bonding [133], charge-transfer interactions [138] and covalent

bonding [134]. In the case of LbL assembly by electrostatic interactions, a substrate is

alternately immersed in aqueous solutions/dispersions of oppositely charged materials,

such as polyelectrolytes, and an extremely thin film is obtained, as thin as at the nanometer

scale [139]. Hu et al., [140] fabricated water purification membranes by layer-by-layer

assembling negatively charged graphene oxide (GO) nanosheets onto a porous

poly(acrylonitrile) support and interconnecting them with positively charged

poly(allylamine hydrochloride) (PAH) via electrostatic interactions. It was observed that 22

in solutions of low ionic strength, the GO membranes retained a tight structure and

exhibited high rejection to sucrose (99%) [140]. In a study by W. Ma et al., [136], a modified electrostatic interaction LbL technique, known as spray and spin assisted layer by layer (SSLbL), was applied to assemble copper nanoparticles (CuNP) functionalized anti-bacterial coatings on a commercial RO membrane. The antifouling coating consisted of multi-layers that employed polyethyleneimine-coated CuNPs as a polycation and poly

(acrylic) acid as a polyanion. By taking advantage of the negative charges on the polyamide surface, the multi-films were firmly deposited onto the membrane and held in place by the resulting electrostatic interactions. SSLbL resulted in a uniform coating of CuNPs on the membrane surface, offered controllable particle loading and also presented a high modification efficiency which indicated the potential for its practical application in commercial anti-biofouling membrane modification practices [136]. Escobar-Ferrand et al., [123] showed the feasibility of preparing defect-free TFC membranes through LbL surface modification of polymeric porous MF/UF membranes using nanoparticles.

Cationic and anionic polyelectrolytes and both spherical (cationic/anionic) and elongated

(anionic) silica nanoparticles were deposited to fabricate crack-free surfaces with thin layers.

Although LBL assembly techniques based on electrostatic interaction are very successful, they often require the preparation of nanoparticles in aqueous solutions [141]. The formation of LbL thin films by covalent bonding offers extra stability to the thin film, which allows it to withstand harsh conditions. [142, 143]. In addition, the presence of an intermolecular interaction enables the incorporation of several other functional groups in the films by reaction with excess reactive groups within the multilayer structure, thus

enabling the design and fabrication of tailored multifunctional assemblies[144]. In another study, M.Hu et al., [145] used the covalent bond LbL mechanism to GO nanosheets, which were cross-linked by 1,3,5-benzenetricarbonyl trichloride (TMC), on a polydopamine- coated polysulfone support. TMC anchored free acyl chloride groups on the support surface, the free acyl chloride groups reacted with the carboxyl or hydroxyl groups in GO to form anhydride or ester bonds. Therefore, the first GO layer was firmly attached to the support by chemical bonds, with TMC working as the cross-linker between polydopamine and GO [145]. When facilitated by hydrogen bonding, LbL assembly provides an avenue for the incorporation of many uncharged compounds into multilayer films. However, this only occurs when substrates that can act as hydrogen bonding donors and hydrogen bonding acceptors are available [144]. Choi et al., [137] used LbL assembly to deposit graphene oxide (GO) nanosheets multilayers on the surface of a polyamide-thin film composite (PA-TFC) membrane to serve as a dual-functional protective layer to improve both membrane antifouling and chlorine resistance, while maintaining the separation performance. A pair of oppositely charged GO nanosheets (positively charged, aminated-

GO (AGO) and negatively charged GO) were alternatingly deposited on the interfacial- polymerized PA membrane surfaces primarily through electrostatic interactions. Besides dominant electrostatic forces, hydrogen bonding between uncharged functional groups

(e.g., amine, carboxylic acid, and hydroxyl groups) on the AGO and GO sheets reinforced the stability of the GO multilayer [137].

Lastly, LbL assembly as a result of charge transfer interactions is achieved by the alternate adsorption of two types of nonionic molecules, which possess electron-accepting and electron-donating groups, respectively, in the side chains [144]. Shimazaki et al., [138],

used two polymers, poly[2-(9-carbazolyl)ethyl methacrylate] and poly[2-[(3,5- dinitrobenzoyl)oxy]ethyl methacrylate], both bearing nonionic pendant groups in the side chains, which have electron-donating character and electron-accepting character, respectively, to create multilayer assemblies. These polymers were alternatively adsorbed onto the gold surface from the solutions in methylene chloride [138].

1.2.3.3. Physical and Chemical deposition

Physical deposition involves the mechanical deposition of nanoparticles without chemical interaction between the polymer and nanoparticles. The two major techniques of physically-depositing nanoparticles within a membrane matrix are by blending [146] and dip-coating [125]. Modification of membranes by blending nanomaterials is a common practical technique for membrane production as no additional processing steps are needed during or after the phase inversion process. Nanoparticles are physically blended into the dope solution before the membrane is synthesized. Several studies reported employing this technique [115, 121, 147-149], but the major problem experienced in these studies is nanoparticle agglomeration and loss of nanoparticles during filtration [146]. In dip-coating, one side of the support is dipped into the nanoparticle suspension until the entire surface is wet and then quickly withdrawn from the liquid. The coated support is allowed to dry at room temperature[150]. Jones et al., [125] employed this technique in making alumina ultrafiltration membranes from alumina nanoparticles (alumoxanes), and the synthesized membranes were defect free. Lin et al.,[151] prepared a series of Nafion/SiO2 composite

membranes via dip-coating surfactant-templated mesostructured silica nanoparticles on

both sides of the Nafion® 117.

Chemical deposition of nanoparticles typically involves either the functionalization of the particles before incorporation in the matrix or the attachment of the particles to the membrane surface as a result of a chemical reaction, which may be a carboxylation [152] or reduction reaction [153]. Lower agglomeration and stronger bonding between the nanoparticle and membrane surface is usually better achieved as compared to physical deposition. In a study done by Huang et al., [126], silver nanoparticles (AgNPs) were in- situ immobilized on polysulfone (PSf) ultrafiltration membranes via polydopamine (PDA) deposition and in-situ reduction of silver ammonia aqueous solution (Ag(NH3)2OH).

Results indicated that the AgNPs were firmly immobilized onto the membrane surfaces as

well as the top layer cross section of the membranes. The adhesive and reductive PDA

layer on the membrane surface induced the reduction of Ag+ without surface pore blockage,

and also favored to the firm attachment and uniform distribution of AgNPs onto the

membrane[126]. Yin et al., [154] studied the immobilization of AgNPs on the surface of polyamide (PA) thin-film composite (TFC) membrane via covalent bonding, with cysteamine as a bridging agent. The synthesized AgNPs were attached onto the membrane surface via the Ag–S chemical bonding. The TFC-S–AgNPs membranes showed that

AgNPs leaching from the membranes was 15.5 mg/cm2 (or approximately 0.7% of the total

membrane sample mass) over a 72-hr filtration period, so nanocomposite membranes were deemed to have good stability of immobilized AgNPs. TFC-S-AgNP membranes also

showed antibacterial properties since after a 7-day biofilm growth test, biofilm formation

was observed on the TFC membrane surface, while the TFC-S–AgNPs membrane surface

was relatively clean and free of biofilm growth [154]. In a different study also on the

chemical deposition of AgNPs on a membrane, Sprick et al., [155] added AgNPs to

cellulose acetate (CA) membranes via attachment with functionalized thiol groups with the

use of glycidyl methacrylate (GMA) and cysteamine chemistries. It was determined that

after 7 days of continuous filtration, little silver leached from the nanocomposite

membranes (37±19 ppb), and no live or dead bacterial cells were observed on the

nanocomposite membranes [155].

Chemical deposition of metal NPs by reduction reaction generally involves transfer of the

desired metal ions by the ion-exchange process to the membrane matrix, and subsequent

reduction of metal ions by appropriate reductant in the membrane matrix [156]. The

reductant plays an important role in the spatial distribution of metal NPs in the

membrane[110]. Bonggotgetsakul et al., [153] prepared AgNPs using a polymer inclusion

membrane (PIM) consisting of 45% (m/m) di-(2-ethylhexyl)phosphoric acid (D2EHPA)

and 55% (m/m) poly(vinyl chloride) (PVC) as a template. The Ag (I) ion was first extracted

into the membrane via cation-exchange and then subsequently reduced using 4 different reducing agents which include sodium borohydride (NaBH4), trisodium citrate, citric acid, and L-ascorbic acid to form AgNPs. The most effective reducing agent was found to be L- ascorbic acid, which formed a uniform monolayer of AgNPs on the surface of the PIM.

Rajaeian et al., [152] experimented on carboxylation of TiO2 nanoparticles to significantly increase their dispersion in aqueous medium. A series of thin film nanocomposite membranes was developed by coating a surface-modified porous poly (vinylidene fluoride)

(PVDF) support with poly (vinyl alcohol) (PVA) doped solution containing TiO2

nanoparticles. In order to improve the interfacial adhesion of nanoparticles in the PVA

blend, an endothermic carboxylation reaction under acidic conditions was carried out on

the TiO2 surface using chloroacetic acid. Carboxylation of TiO2 nanoparticles was carried

out by the reflux method. The carboxylation of TiO2 nanoparticles promoted particle

dispersion within the PVA doped solution with significantly reduced particle

agglomeration. Without the surface carboxylation, there was only weak coordination

+ between Ti4 and the hydroxyl groups on the PVA surface which weakly bonded the TiO2

agglomerates. On the other hand, the covalent crosslinking between the carboxylic groups

at the modified TiO2 surfaces and PVA hydroxyl chains provided a strong and irreversible binding force to embed nanoparticles inside or onto the PVA surface. The nature of the bonding between the carboxylic groups and PVA chains was likely the hydrogen bonding, although a small amount of esterification may also have occurred. The new carboxylated thin film nanocomposite membrane had improved performance including solute rejection, antifouling properties and flux recovery ratio [152].

1.2.3.4. Chemical grafting

Chemical grafting of nanomaterials involves the transformation of the nanocrystals into a

continuous material through long chain surface chemical modification using grafting

agents bearing a reactive end group and a long compatibilizing tail [157]. Song et al., [158]

prepared ultrafiltration membranes from PSf composites with poly(1-vinylpyrrolidone) grafted silica NPs (PVP-g-silica). For the synthesis of PVP-g-silica, hydroxyl terminated silica NPs were reacted with (3-methacryloxypropyl) trimethoxysilane (γ-MPS) to form γ-

MPS terminated silica NPs (silica-MPS), which were further reacted with a vinylpyrrolidone (VP) monomer via a wet phase inversion process. PVP-g-silica nanoparticles exhibited better dispersion in the PSf matrix and interfacial adhesion with

PSf than pristine silica nanoparticles. In the study done by Liang et al., [159], pristine

PVDF membranes were grafted with poly (methacrylic acid) (PMAA) by graft 28

copolymerization, providing sufficient carboxyl groups as anchor sites for the binding of

silica NPs. Sawanda et al., [117] used a modified chemical grafting technique to incorporate AgNPs onto the membrane surface. In –this study, acrylamide was grafted onto a PES membrane surface and AgNPs were formed within the grafted layer by reducing the silver ions with sodium tetrahydroborate aqueous solution. Geng et al., [124], synthesized an anti-photocatalytic ageing poly(aryl ether sulfone) polymer matrix containing trifluoromethyl groups and carboxyl groups (PES-F-COOH). TiO2 clusters were covalently

incorporated into the fluorine-containing poly (aryl ether sulfone) matrix via a side chain

grafting reaction using a silane coupling agent. The strong attachment of TiO2 clusters to

the polymer matrix resulted in a homogeneous dispersion. The prepared TiO2/PES-F-

COOH hybrid ultrafiltration membranes exhibited excellent separation, anti-fouling, and self-cleaning properties, while resistant to decomposition by photocatalytic oxidation.

Lastly, Yang et al., [160] modified a TFC polyamide nanofiltration membrane by grafting poly(2-hydroxyethyl methacrylate) (polyHEMA) chains from the surface of the membrane.

A modified Gabriel synthesis procedure[160] was used to attach superparamagnetic

(Fe3O4) nanoparticles to the chain ends. Nanoparticles were attached to the membrane

surface by reacting carboxyl groups on the nanoparticle surface to the primary amine at the

polyHEMA chain ends via an amide linkage. Modified membranes display both increased

permeate fluxes and increased salt rejection in the presence of an oscillating magnetic field

compared to their performance in the absence of an oscillating magnetic field.

1.2.3.5. Other methods for fabrication of surface located nanocomposite membranes

Corona plasma-assisted coating TiO2 nanoparticles is a useful technique for modification

of polymeric membranes to improve separation and antifouling properties. Moghimifar et

al., [119] modified the surface of polyethersulfone (PES) ultrafiltration membranes by

corona air plasma and by coating TiO2 nanoparticles. For this purpose, the TiO2

nanoparticles, were coated on the surface of the corona plasma treated PES membranes,

which were prepared via the non-solvent-induced phase inversion method. TiO2

nanoparticles were coated on the membrane surface by immersion of the corona treaded

membranes into a TiO2 colloidal aqueous solution [119]. Liu et al., [161], prepared a

composite membrane formed from reduced graphene oxide (RGO) and AgNPs via a rapid

thermal reduction method. The average diameter of the AgNPs was approximately 20–40

nm. The RGO membranes and RGO–AgNP composite membranes were prepared by

vacuum filtration of RGO–AgNPs dispersions through mixed cellulose filter membranes.

The membrane with the mass ratios 1: 2 of AgNO3 to GO had the best combination

performance due to its suitable distribution of silver nanoparticles. Mohamad et al., [162]

studied the performance of polyethersulfone (PES) ultrafiltration membrane coated with

titanium dioxide (TiO2) nanoparticles and irradiated with UV light. Flat sheet membranes

were prepared via phase inversion, with two types of membranes including TiO2 coated

PES membranes and UV-irradiated TiO2 coated PES membrane. TiO2 suspensions were

prepared and coated on the PES surface via dip coating, and then, prepared membranes

were irradiated. Results indicated that the pure water flux and humic acid permeation of

UV irradiated TiO2 coated membrane was higher than TiO2 coated membrane. In the study

performed by Yang et al., [163], zeolitic imidazolate framework (ZIF-8) nanoparticles

were in-situ growth onto the surface of GO sheets to form ZIF-8@GO composites, which

were co-deposited with polyethyleneimine (PEI) matrix on a tubular ceramic substrate

through a vacuum-assisted assembly method. ZIF-8@GO laminates were embedded in PEI

matrix under the transmembrane pressure. PEI was used as a bridging agent to improve the

bonding force between separation layer and the substrate. Moreover, PEI was easy to be

chemically cross-linked because of the abundant amine groups in its molecular chains. The

obtained composite membrane was then cross-linked with glutaraldehyde (GA) to make it

more stable.

1.3. Per- and polyfluorinated chemicals (PFAS)

Per- and polyfluoroalkyl substances (PFAS) are a type of synthetic chemical found in the

environment that are toxic to many ecosystems as well as humans. As a result, locations

contaminated by PFAS are becoming more heavily regulated by various government

organizations. Effective methods of their removal are thus necessary to reduce their

prevalence and negative effects on the environment. PFAS are carbon chains with one or

more fully fluorinated carbon (polyfluoroalkyl) or all fully fluorinated carbons

(perfluoroalkyl) [1]. Figure 9 shows the structure of a PFAS compound. The carbon chains have a terminal functional group, most commonly carboxylic acids and sulfonic acids abbreviated as (PFCAs) and (PFSAs) respectively. Additionally, PFAS are categorized by their carbon-chain length as short-chain, PFCAs with seven or fewer carbons and PFSAs with five or fewer carbons, or long-chain, PFCAs with eight or more carbons and PFSAs with six or more carbons. Longer carbon-chain length leads to an increase in the PFAS bioaccumulation. PFSAs can bioaccumulate more than PFCAs, this fact is responsible for the smaller carbon-chain length for PFSAs to qualify as short-chain than PFCAs. PFAS

were originally synthesized by 3M in the 1940’s, and were used commonly because of their

water-, stain-, and grease-resistance [165].These qualities improved the functionality of

many products including waterproofing materials, firefighting foams, and general

household goods.

Figure 9: Perfluorooctane sulfonic acid (top image); Perfluorooctanoic acid (bottom image)

Their introduction into the environment has been facilitated by the decomposition of

products containing PFAS, as well as their emission from perfluorochemical factories.

The treatment technologies currently available for the removal and/or degradation of PFAS compounds are limited to adsorption, advanced photochemical oxidation, sonochemical decomposition, filtration, and air-sparged hydrocyclone technology[166]. Technologies such as oxygenation to induce aerobic conditions and some forms of chemical oxidation

have been shown to breakdown perfluorinated acids [167]. Figure 10 summarizes some current treatment technologies used for the removal of PFAS compounds.

Figure 10: Current treatment technologies for PFAS removal [167] For adsorption, removal of PFAS occurs by electrochemical interactions and hydrophobic

interactions with the polar and nonpolar groups of PFAS [168]. Some adsorption

techniques include biosorption, granular activated carbon, anion exchange, and non-ionic

resins [168].In the absence of organic matter, they are effective for the removal of long

chain perfluoroalkyl acid but ineffective against short chain perfluoroalkyl acids [167].

Sonolysis involves the use of ultrasound waves to create cavitation. During the process of cavitation, bubbles collapse and adiabatically generate high pressure and temperature conditions that pyrolyze perfluorinated compounds [169]. Sonolysis has been very successful for the breakdown of PFAS compounds at the laboratory scale, but it has not been commercialized because of design challenges during the cavitation propagation [167].

Advanced oxidation processes that have successfully degraded PFAS include ultraviolet

(UV) irradiation and electrochemical techniques [170]. Photochemical oxidation is an

indirect photolysis technique which degrades contaminants by reacting with reactive

radicals. Adding a photocatalyst to UV photolysis of PFAS greatly enhances the ability of

2 3 2− 4- the process to degrade the material [171]. Catalysts such as TiO , Fe +, S2O8 , IO , and

2− CO3 , in combination with UV can efficiently degrade PFAS owing to formation of

reactive and potent oxidative species such as CO3- • , H• , OH• , and PFAS complexes

[172]. Direct photolysis of PFASs tends to have relatively low removal efficiencies and fluoride yields compared with other processes and thus needs additional processes to complete degradation [171]. Filtration techniques are centered around membrane-based systems. Reverse osmosis and nanofiltration have been shown to attain high rejection values, over 99% in some instances. The mechanism for PFAS removal is usually controlled by size exclusion, adsorption or charge interactions [168]. A shortcoming of this technique is the creation of highly concentrated retentate that requires treatment or disposal. Air-sparged hydrocyclone technology involves the use of coagulants with wastewater containing PFAS compounds to create bubbles after spinning at high pressure

and air extraction in the reverse direction of the spin. This leads to the removal of the PFAS

contaminant. The technique has an efficiency of 70% and involves numerous steps to

achieve minimum contaminant levels [173].

CHAPTER 2. Research Objectives

The overarching goals of this project were to first show that phosphorene possesses

catalytic properties to destroy organic compounds, such as dyes and PFAS compounds,

and that its electrical conductivity is anti-microbial, and then, to develop low fouling novel

nanocomposite membranes holistically from the initial investigation of phosphorene to

testing. To this end, the research was built around two hypotheses.

2.1. Hypotheses

A) Photocatalysts absorb photons to increase the chemical rate of reaction [174].

Reactions are activated by the absorption of a photon with sufficient energy (equivalent to

or greater than the band-gap energy of the catalyst). The photon absorption leads to a charge

separation due to elevation of an electron (e−) from the valence band of the semiconductor

catalyst to the conduction band[175]. Phosphorene exhibits characteristics that are

desirable for photocatalytic applications which include quantum confinement in the

direction perpendicular to the 2D plane signifying optical properties, large lateral size with

a high specific surface area and ratio of exposed surface atoms, and a high absorbance and

strong interaction with light [176-179]. Furthermore, phosphorene is a direct and narrow band gap semiconductor, thus, it could efficiently harvest low energy photons during photocatalysis, which can be tuned appropriately for photon absorption in the ultraviolet, visible light and the near-infrared region of the solar spectrum. Hence, it is hypothesized that phosphorene can act as a metal-free photocatalyst to degrade organic compounds in the feed solution to make the membrane self-cleaning.

B) On a conductive surface over which a field is applied, adhesion of bacterial cells

can be prevented. When a positive charge is applied, it stimulates an oxidizing environment

for the bacteria, thus increasing bacterial surface mobility and preventing bacteria from

adhering to the surface. Conversely, a negative charge produces a repulsive electrostatic

force between the like charged bacteria and the surface. Thus, applying alternating charges

to a surface efficiently prevents bacteria from forming a biofilm [180].

To investigate these hypotheses, the objectives of this study are as followed:

Objective 1: Exfoliation and stabilization of phosphorene

Phosphorene was chemically exfoliated from bulk black phosphorus by sonication and

centrifugation. A basic exfoliation technique in sodium hydroxide/ N-methyl pyrrolidinone was chosen that produced a uniform dispersion of phosphorene in the exfoliation medium.

The phosphorene nanoparticles synthesized exhibited high yield and high stability in water.

By a substitution reaction, a hydroxide molecule was attached to phosphorene thus

impacting a negative charge on the surface making it stable in water. This was addressed

in chapter four.

Objective 2: Immobilization of phosphorene and synthesis of polymeric membrane

A blend of polymers was made from polysulfone and sulfonated poly ether ether ketone

and a homogeneous dope solution was prepared with N-methyl pyrrolidone. Poly ether ether ketone (PEEK) was converted to sulfonated poly ether ether ketone by an electrophilic aromatic sulfonation reaction. Phosphorene was physically immobilized into the dope solution to form a membrane and a flat sheet, mixed matrix, nanocomposite membrane was synthesized by immersion precipitation during the phase inversion process. 36

These membranes were characterized via membrane autopsies for morphological and structural changes. This was addressed in chapter four and five and six.

Objective 3: Determination of the catalytic properties of phosphorene

The ability of phosphorene to degrade organic compounds in the presence of light was investigated. Phosphorene-modified membranes were used as the photocatalyst to photodegrade methylene blue under ultraviolet (UV) and visible irradiation. These membranes were also used to degrade per- and polyfluoroalkyl substances. The photocatalytic ability and level of degradation of MB using phosphorene was analyzed by fluorescence microscopy. This was addressed in chapter four and six and seven.

Objective 4: Contaminant removal

Perfluorooctanoic acid was used to examine the capability of phosphorene for contamination removal. After filtration, the contaminated phosphorene membranes were analyzed for levels of reversible and irreversible fouling propensities. The membranes were also subjected to a secondary treatment via photolysis with ultraviolet irradiation and oxygenation in aerobic conditions to destroy the contaminant. This was addressed in chapter six.

Objective 5: Determination of the biocidal properties under an alternating electrical potential

SPEEK and phosphorene-based membranes were synthesized and analyzed using cross- flow filtration to determine their biocidal properties. Serratia marcescens was the model bacteria and filtration was performed under alternating positive and negative voltage bias

conditions. The biofouled membranes were examined for bacteria growth after three days.

This was addressed in chapter seven.

CHAPTER 3. Materials and Experimental

3. Methodology

3.1. Materials Black phosphorus used for the synthesis of phosphorene was purchased from Smart

Elements (Vienna, Austria) and the ultrasonicator model P70H was purchased from

Elmasonic P, Singen, Germany. For the sulfonation reaction, polysulfone (PSf), N-methyl

pyrrolidone (NMP), poly ether ether ketone (PEEK), and concentrated sulfuric acid were

purchased from VWR (Radnor, PA, USA). Methylene blue was purchased from VWR,

Radnor, USA. Sodium hydroxide (NaOH), bovine serum albumin (BSA), sodium chloride

(NaCl), phenolphthalein indicator and citric acid were also purchased from VWR, Radnor,

USA. A dead-end cell, Amicon Stirred Cell 8010–50 mL, was purchased from EMD

Millipore, Burlington, MA, USA. Perfluorooctanoic acid (PFOA) was purchased from

Sigma Aldrich (St Louis, MO, USA). For the biofouling experiments, the bacterial strain,

Serratia marcescens was purchased from ATCC (Manassas, VA, USA). The ingredients used to prepare the nutrient agar solution (DifcoTM Nutrient broth, agar powder and sodium chloride (NaCl, 99.5%), were purchased from VWR (Radnor, PA, USA). For membrane filtration studies, the dead-end cell, Amicon Stirred Cell 8010–50 mL, was purchased from EMD Millipore (Burlington, MA, USA). The cross-flow filtration cell was purchased from Sterlitech (Kent, WA, USA).

3.2. Preparation of phosphorene from black phosphorus.

Liquid exfoliation is a very promising typical method that has been extensively used to prepare ultrathin 2D nanoparticles. The liquid exfoliation of black phosphorous was carried out using previously developed methods [22]. Bulk black phosphorus (15 mg) was added

to a NaOH/NMP solution (30 mL). The mixture was put in a sonicator (Elma Elmasonic

P, Germany) operated at 37 kHz frequency and 80% power for 4 hours for the liquid

exfoliation of bulk BP. After exfoliation, the solution was centrifuged at 3000 rpm for 10 min to remove any non-exfoliated bulk BP. The supernatant was then centrifuged at 4000 rpm for another 20 min to separate the relatively thick phosphorene from the NMP. The precipitations obtained by the two separation processes were redispersed in water and the

solutions were washed in deionized water. Finally, 0.05 mL of the thick and thin

phosphorene water solutions were dropped onto silicon with a 280-nm SiO2 surface layer

(1 cm × 1 cm). Raman studies were carried out on silicon after drying in a vacuum dryer

(Cole-Parmer, Vernon Hills, IL).

3.3. Preparation of sulfonated PEEK.

PEEK polymer was sulfonated using procedures reported in the literature [181, 182]. PEEK was dried in a vacuum oven at 100◦C for 24 hrs. Thereafter, 25 g of PEEK was dissolved in 250 ml of concentrated sulfuric acid (95–98%) and vigorously stirred at room temperature for 3 days. Then, the polymer solution was gradually precipitated into ice-cold water under mechanical agitation. The polymer suspension was left to settle overnight. The polymer precipitate was filtered, washed several times with distilled water until the pH became neutral, and dried under vacuum at 60◦C for 24 h. Figure 11 shows the sulfonation process

Figure 11: Sulfonation of PEEK to SPEEK [183].

3.4. Determination of Degree of Sulfonation The degree of sulfonation (DS) is the content of hydrogen sulphite present after all possible

substitution for hydrogen sulphite has occurred on all points in the substitution site[184].

For SPEEK, sulfonation usually happens on the phenyl ring located between the two ether

groups of the PEEK repeat unit[185]. SPEEK with a high degree of sulfonation (DS) has a

relatively low chemical stability[186]. Hence, it is necessary to calculate DS. To

quantitatively determine the DS, the 1H NMR spectra of SPEEK in a deuterated solvent, dimethyl sulfoxide (DMSO-d6) was carried out. At a frequency of 400MHz, a Bruker

(Billerica, MA, USA) Avance NEO spectrometer equipped with a Smart Probe was utilized for this experiment. 5wt% of SPEEK was dissolved in DMSO-d6. The internal standard

used was DMSO at 2.5 mg/L. The assignment of the peak signals was from literature[187].

The presence of –SO3H group after substitution results in a down field shift of the nearest

neighboring proton (H10) as seen in Figure 12. Using equation 3, the DS was estimated from the ratio between the peak area of H10 and the total integrated peak area of all the remaining aromatic protons (Hx, where x =1,2,3,4,5,6,7,8,9,11).

( ) = = ( 0 ≤ y ≤ 1)[184] (3)

𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷 𝒂𝒂𝒂𝒂𝒂𝒂𝑷𝑷 𝒐𝒐𝒐𝒐 𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 𝑯𝑯𝟏𝟏𝟏𝟏 𝒚𝒚 𝑨𝑨 𝑨𝑨𝑨𝑨𝑨𝑨 𝒐𝒐𝒐𝒐 𝑯𝑯𝟏𝟏𝟏𝟏 ∑ 𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷 𝒂𝒂𝒂𝒂 𝒂𝒂 𝒂𝒂 𝒐𝒐𝒐𝒐 𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 𝟏𝟏𝟏𝟏−𝟐𝟐𝟐𝟐 ∑ 𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨 𝒐𝒐𝒐𝒐 𝑯𝑯𝑿𝑿

Figure 12: Nomenclature of aromatic protons of SPEEK

3.5. Membrane preparation

In the process of membrane formation via phase inversion, a membrane is made by casting a polymer solution on a support and then bringing the solution to phase separation by means of solvent outflow, and/or nonsolvent inflow. Thus, in most cases at least three components are involved: a polymer, a solvent, and a nonsolvent [188]. During the phase inversion process, a thermodynamically stable polymer solution is converted from a liquid into a solid state in a controlled manner. This solidification is preceded by a liquid–liquid demixing. A certain time after initiation of the demixing into a polymer-rich and a polymer- lean phase, the phase with the highest polymer concentration starts solidifying through processes like gelation or crystallization. The polymer-lean phase leads to the pores in the solidified material, while the polymer-rich phase leads to the solid membrane matrix [189].

The blended polymer dope solution was prepared by dissolving PSf and SPEEK (95/5%) into NMP. Exfoliated black phosphorus was added to the solution (0.5% wt. volume) and sealed with parafilm to prevent air bubbles from being trapped inside the solution and affecting the homogeneous mixing of the solvent and the solute. The blended solution was placed on a magnetic stirrer and heated at 65˚C for 2 days. It was degassed in a sonicator to get rid of air bubbles for 1hr. The blended solution was spread on a glass plate with a 42

doctor blade at a wet thickness of 0.250 mm and exposed to air for 12 s. A clean glass

mirror was used as a surface, which provides optimum hydrophobicity to the membranes

and helps for detachment of polymer films during phase inversion [190]. The glass plate

and dope solution were immersed in a coagulation bath of deionized water and the

membrane was formed via the process of phase inversion. The membranes formed were

subsequently washed thoroughly with deionized water to remove residual solvent and kept

in deionized water before testing.

3.6. Membrane Characterization

3.6.1. Flux Analysis Dead end filtration was used to monitor the flux decline of the membrane. Filtration

experiments were performed using Amicon filtration cell (Amicon Stirred Cell 8010 – 50

ml). Using a constant membrane surface area of 13.4 cm2, the time to collect a 2-ml permeate sample was measured for each feed and flux was calculated. A constant pressure of 20 psi (1.37 bar) and continuous stirring were applied in all tests. Flux values were calculated as L/m2-hr from equation 4 and plotted against the total time of filtration.

Membrane samples were cut into circular pieces of area 13.4cm2 and supported by a

WhatmanTM filter paper (110 mmø). Each membrane was precompacted with DI water

until a stable flux was reached. Precompaction was followed by filtration of protein

solutions of 1000 ppm each of bovine serum albumin (BSA) protein in water. The

concentrations of the proteins were determined using a total organic carbon analyzer

(Teledyne Tekmar Fusion, Mason, Ohio) and the protein rejection was calculated

according to following equation[191]:

= 1 × 100% (4) 𝐶𝐶𝑝𝑝 𝐶𝐶𝑓𝑓 where Cp and Cf are𝑅𝑅 solute� concentrations− � in permeate and feed solutions, respectively.

After water filtration, reverse flow filtration using DI water was performed to remove

reversibly-attached foulants that were not adsorbed to the membrane, and the filter paper

support was changed. The flux recovery of the membrane was measured afterwards.

3.6.2. Contact angle measurement

Contact angle is defined as the measure of wettability of a surface. A drop shape analyzer

(Kruss DSA100, Matthews, NC) was used for the contact angle measurement of all the

membrane samples. A small drop of water was placed on the membrane surface and

resultant angle of the droplet to the surface was measured [192]. The higher the

hydrophobicity of the membrane, the higher the contact angle.

3.6.3. Zeta potential

Zeta (ζ) potential is the potential in the interfacial double layer (DL) at the location of the

slipping plane versus a point in the bulk fluid away from the interface. It is the potential

difference between the dispersion medium and the stationary layer of fluid attached to the

dispersed particle [193]. It is used to characterize the surface charge property of membranes

at different pH environments. This analysis is particularly important to understand the acid- base properties and to predict the separation efficiency of membranes [194]. Surface charge is analyzed by measuring the zeta potential using an Anton Paar SurPASS electrokinetic analyzer (Anton Paar, Ashland, VA) in surface analysis mode. Before analysis, membranes are rinsed with copious amounts of DI water to remove any residual solvent. The KCl

electrolyte solution used in these measurements has an ionic strength of 1.0 mM. The pH

values for the various readings are adjusted using 0.5 M NaOH and 0.5 M HCl solutions.

3.6.4. Raman Studies

When light is scattered from a molecule or crystal, most photons are elastically scattered.

The scattered photons have the same energy (frequency) and, therefore, wavelength, as the

incident photons. However, a small fraction of light is scattered at optical frequencies

different from, and usually lower than, the frequency of the incident photons. The process

leading to this inelastic scatter is termed the Raman effect. Raman scattering can occur

with a change in vibrational, rotational or electronic energy of a molecule. Raman

scattering occurs only when the molecule is polarizable. If the scattering is elastic, the

process is called Rayleigh scattering. If it’s not elastic, the process is called Raman

scattering [195, 196]. Raman spectroscopy is a vibrational technique. The number of

normal modes of vibration of a molecule with N atoms can be determined from the

displacements of each atom in the x, y, and z directions. There are 3N such displacements,

but 3 of these result in translation of the whole molecule in the x, y, and z directions, and

3 result in molecular rotations. Thus the molecule has 3N-6 normal modes of vibration [

3N-5 if the molecule is linear, since there is no rotation possible about the molecular

axis[197]. Symmetry species of translations, rotations, and vibrations can be determined

by considering the character of the representation spanned by Cartesian vectors localized

on each atom[198]. In a crystal, these vibrations are observed as phonons. In an inelastic process, like the Raman scattering, light is scattered and a phonon or normal mode is created or destroyed[199]. For a vibration to be active in a Raman spectrum, the vibration

must change the polarizability of the molecule. Using the group theory and character tables, vibrational modes can be assigned to a molecule. Raman spectroscopy has been widely used to understand the electronic and vibrational properties, as well as their dependence on the thickness of various 2D layered materials [200, 201]. Raman spectroscopy is a very practical tool for quickly identifying molecules and minerals. The pump radiation was supplied by a laser operating at a wavelength of 632 nm; the Raman emission was collected by a 100x objective in a backscattering geometry.

3.6.5. Liquid-Liquid Porometer studies

In liquid-liquid displacement porometry (LLDP), a pair of immiscible liquids with low interfacial tension is used. The procedure is to wet the membrane with one liquid, the wetting liquid, and then displace it with the other. By measuring the pressure and the flow through the membrane, the corresponding pore radius can be calculated using the Cantor equation in equation 5[202].

= (5) 2𝛾𝛾𝛾𝛾𝛾𝛾𝛾𝛾𝛾𝛾 𝑃𝑃 � 𝑟𝑟𝑝𝑝 � where P is the pressure, γ the interfacial tension, θ the contact angle and rp the pore radius.

The contact angle is assumed to be zero. The LLP-11000A by PMI, Ithaca, NY, was used in this experiment. Isopropanol was used as the displacing liquid and sliwick oil as the membrane-wetting liquid.

3.6.6. Morphological characterization

Environmental scanning electron microscopy (ESEM) was used to verify the asymmetric

morphology of the membranes and monitor the surface of both unmodified and modified

membranes. A FEI Quanta 3D FEG Dual Beam Electron Microscope (FEI, USA) was used

to test the samples. By freezing small samples of the membranes in liquid nitrogen and

cracking them, smooth cross-sectional areas could be observed. To obtain an image of the

cross-section of the membranes, the frozen and cracked samples were attached vertically

to a carbon tape while the samples were attached horizontally to the carbon tape to get an image of membrane surface. The surfaces of the samples were dusted with a thin layer of palladium-gold using a Cressington 108 auto sputtering device and then observed under

scanning electron microscope. The Quanta has an Energy Dispersive X-ray spectroscope

(EDX) attached to it, so the EDX analysis was also performed on the sample.

3.6.7. Fourier-Transform Infrared Spectroscopy (FTIR)

FTIR is commonly used in the study, identification, degradation and characterization of

polymeric structures[203]. Molecules can absorb light in the infrared region that usually

translates into changes in the vibrational frequency[204]. Apart from diatomic elemental

gases, all compounds exhibit infrared spectra and can be analyzed qualitatively by their

distinctive infrared absorption[204]. Functional groups possess characteristic infrared

absorption bands that are synonymous to the stretching, contracting, and bending vibrations

of the functional groups. These vibrations are expected within specific regions on the

spectra and are influenced by the kind of chemical bonds present in the functional group,

as well as the atoms which make up the group[205]. The infrared region of the spectra is

divided into three basic regions which are the near-IR, mid-IR, and far-IR. The mid-IR, which falls under wavelength numbers spanning from 400 up to 4000 cm-1, is where most

chemical molecules absorb frequencies and exhibit vibrations [206].

3.6.8. Transmission Electron Microscopy (TEM) and HAADF-STEM

Exfoliated phosphorene samples were prepared and added dropwise onto a carbon film on

a copper grid (Lacey carbon film, 300 Mesh Cu, TED Pella Inc.). The lacey carbon film

was then left in a hood overnight to completely dry the solvent. High-resolution

transmission electron microscopy (HR-TEM) was performed on a FEI Talos F200X

instrument operated at an accelerating voltage of 200 kV and with a point-to-point

resolution of 0.1 nm. The TEM images were obtained at typical magnifications of 100 K

to 1.05 M. Velox digital micrograph software was used to analyze the samples and Image

J was used to estimate nanoparticle size. Scanning transmission electron microscopy

(STEM) was performed on the same instrument (FEI Talos F200X, using a high angle

annular dark field Detector (HAADF) at 200kV. HAADF-STEM image intensity is

reported to be proportional to square of the atomic number, so heavy atoms are observed

brighter. The phosphorene nanoparticle composition and element distribution were

determined via FEI super energy-dispersive X-ray spectroscopy (EDX) system.

3.6.9. Optical Profilometer

The surface morphology of membranes influence the fouling pattern, membrane

permeability as well as the solute rejection of the membrane[207]. Studies have shown

that smoother surfaces tend to exhibit lower rejection and higher flux values, whereas,

rougher surfaces exhibit higher rejection and lower flux values[208]. Atomic force

microscopy (AFM) is the most common technique used for characterization of membrane

surface roughness because of ease of use and functionality in different environments[209], but a major drawback is the limitation on scan surface area. Given that surface roughness is a function of scan size, a small scan area may be misrepresentative of the true overall surface roughness[210]. Optical interferometry on the other hand, provides roughness information over a larger scan size and thus more accurate information can be deduced on the membrane surface roughness[209]. Optical profilometers are used to evaluate height variations on surfaces hence information on the surface roughness of the surface can be obtained. They are interference microscopes that utilize the wave properties of light to compare the optical path difference between a test surface and a reference surface. Surfaces can be characterized quickly and precisely to determine surface roughness, critical dimensions, and any additional topographical features. Measurements made are usually nondestructive and do not require sample preparation. The Zygo New View 7000 optical profilometer (Zygo Corporation, Middlefield CT, USA) was used to characterize the surface of the phosphorene modified membrane as well as the unmodified membrane. The scan length was 65 µm bipolar (20 secs) and the magnification of the objective lens was

50x. Two dimensional and three-dimensional images were obtained for analysis.

3.6.10. Surface roughness characterization

For nanofiltration membranes, factors that affect the extent of fouling irrespective of foulants on the membrane include membrane surface roughness, surface charge and surface hydrophobicity[211]. The surface roughness of the membranes were measured after reverse flow filtration to determine the effect of PFOA fouling on the roughness of the

membrane. An atomic force microscope (AFM) (Bruker Dimension Icon, Santa Barbara,

CA, USA ) was used. A membrane area of 20 × 20 µm was chosen. Data were collected under peakforce tapping mode and evaluated by the average root-mean-squared (RMS) roughness

3.6.11. Surface Fluorescence Characterization

To determine the level of fouling by MB after each experiment, the membranes were imaged under a fluorescent microscope. Images where recorded on a Zeiss 880 NLO upright confocal microscope (Thornwood, NY, USA) with a 10 × air objective. The membranes were sandwiched between microscope slides and wetted with water for smoothing them out. Tiles, showing the full field of over a z-range to cover the slightly non-planar geometry of the membrane, were stitched together in a format of 3×3, reflecting a representative cover. Methylene blue was excited with a 633 nm laser and emission was collected over a spectral range of 642 to 759 nm.

3.7. Leaching Studies

The stability of static phosphorene within the pores of the membrane was examined using a cross flow cell, the schematic is shown in Figure 13 in recycle mode. The feed solution, deionized water, was stirred at a rate of 200 rpm. The phosphorene-imbedded membrane was left in continuous contact with the deionized water flowing through the cell for fifteen days. Samples were taken daily from the beaker and tested for presence of phosphorus using an inductively coupled plasma atomic emission spectroscopy (ICP-OES). During the membrane formation process via phase inversion in a water bath, samples of the remnant water-solvent mixture were obtained and tested for phosphorene. Furthermore, the stability

of the phosphorene membranes at various pH levels was tested at room temperature. For

the stability studies, concentrations of phosphorene in the dope solutions were 650, 800

and 1000 mg/L. Phosphorene membranes with an area of 100 cm2 were left in 100 ml of

citric acid at pH 4, sodium hydroxide at pH 13, and deionized water at pH 7, respectively

for 72 hrs. and samples were collected and analyzed for phosphorus using the ICP-OES.

The detection limit was 60ppb.

Figure 13: Schematic of Leaching Study Setup

3.8. Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) Study

A Varian Vista Pro CCD simultaneous ICP-OES was used to determine the concentration of phosphorus in permeate samples. The power used was 1.2kW, plasma flow rate of 15

L/min, auxiliary flowrate of 1.5 L/min, nebulizer flowrate of 0.9 L/min, the replicate read

time was 35 s and the instrument stabilization delay was 20s. Samples were acidified to a

pH <5.5. A 25-ppb analytical detection limit was established with phosphorus calibration 51

standards prepared in 1% HNO3. Standard curve correlations maintained a correlation

coefficient > 0.995. Sample measurements were read in triplicate. Quality control measures

included a diluent blank, standard control, and yttrium internal standard measurements with

each sample reading. The ICP-OES was also utilized to measure phosphorous

concentrations in free phosphorene exposure solutions used in toxicity testing (described

below) as well as in permeates generated by filtering media through phosphorene membrane.

3.9. Toxicity Testing

For toxicity testing phosphorene was transferred from solvent into DI water for triple

washing. The washing steps required centrifugation at 12,000 g for 20 min, removal of

supernatant leaving phosphorene pellet intact on the bottom of the tube and replenishing

with DI water. After third wash, the exposure medium was added. Two media used for the

exposures were 50% K-Medium (31.68 mM KCl and 51.37 mM NaCl) and Moderately

Hard Reconstituted Water (MHRW; KCl 4 mg/L, MgSO4 60 mg/L , CaSO4 60 mg/L,

NaHCO3 96 mg/L) [212] . The protocols for toxicity screening have been modified from previously established C. elegans toxicity testing methods [213, 214] . Wild-type N2 strain of C. elegans were obtained from Caenorhabditis Genetics Center (CGC). The nematodes were age-synchronized and the eggs placed on K-agar plates with Escherichia coli OP50 as a food source [215] . For mortality, the L3 stage nematodes were exposed to concentration range of Phosphorene from 0 to 60 mg/L in two media, 50% K-medium and

MHRW. The 24-well tissue culture plates were used for exposures with 1 mL of the solution and 10 (±1) nematodes per well, with 4 replicates per concentration. Mortality was

scored after 24 h. The testing for all concentrations was conducted in two independent experiments. For reproduction, eggs were hatched on K-agar plates with E. coli OP50 bacterial lawn, and after 24 h the nematodes at F2 stage were placed into the exposure solutions for 24 h. In each treatment, the nematodes were exposed to four sub-lethal concentrations of Phosphorene in 50 K-Media or MHRW. The exposures were conducted in the presence of bacterial food, E. coli OP50 at OD600=1 and 10 ul per ml of exposure solution. After exposures individual nematodes were placed on K-agar plates containing

E. coli OP50 and allowed to reproduce. The adults were transferred to the new K-agar plates every 24 h up to 72 h. The offspring that remained on the plate were allowed to hatch and grow for 24 h and after that were stained with Rose Bengal (0.5 g/L) and heated at 55

°C for 50 min. The stained offspring were counted under microscope. The mortality testing were also conducted with 1, 3, and 5 order of permeates generated after filtering K-medium or MHRW through phosphorene membrane.

3.10. Biofouling Studies

To study the antimicrobial properties of phosphorene, fouling studies were done using

Serratia marcescens subsp. marcescens Bizio (ATCC 13880). Serratia marcescens subsp. marcescens was selected to investigate the inhibitory effect of different phosphorene modified membranes on bacterial growth. BactoTM tryptic soy broth (Becton, Dickinson, and Company) was prepared based on the manufacture’s direction, then autoclaved to remove all possible bacterial contamination, and used as a growth media to culture Serratia marcescens. Bacterial solution was prepared by overnight growth of Serratia marcescens at 27℃ in tryptic soy broth. The number of bacteria was counted after serial dilution on

tryptic soy agar which was 9.5 × 108 CFU/mL. Assessing the bacterial growth in the

presence of different membranes was investigated on DifcoTM tryptic soy Agar (Becton,

Dickinson and Company). Agar solution was prepared and autoclaved to remove all bacteria. Then, agar plates were prepared aseptically by adding autoclaved agar solution into each plate under a laminar flow hood.

To investigate the specific role of electrical potential in bacterial detachment and inactivation when a voltage is applied through phosphorene, the bacteria solution was then filtered through the membrane. The filtration experimental setup consisted of a custom built cross-flow filtration cell (Sterlitech CF016A, Kent, WA) designed with built-in insulated titanium electrodes capable of delivering an electric charge to the membrane thin film surface (effective membrane surface area was 21.6 cm2). The electrodes were

connected to a voltage generator (Circuit Specialists CS15003X5, Tempe, AZ). During

operation, a peristaltic pump (Varian Prostar 210, Santa Clara, CA) was used to deliver a

pressurized feed stream at 4.13 bar over the membrane. Experiments were done under no

charge and then alternated positive and negative signal at 1.5V for 1 minute each. This was

done for thirty minutes. This was done on unmodified and phosphorene-modified membranes. After filtration, the membranes were placed on an agar plate and left for 3 days. One agar plate was considered as a negative control to verify negative bacterial growth on the prepared agar under sterile condition. Membrane sterilization was done by rinsing the membranes with alcohol. To verify the membrane sterilization process, one negative control plate was considered for each membrane by laying a sterile membrane

[round, 21.6cm2] from the last part on the prepared sterile agar plate. Then the negative

control was incubated for 24 hours at 27℃. The negative growth of bacteria on the

membrane verified the membrane sterilization with alcohol. Three positive controls were

prepared by adding 10 ml of Serratia marcescens on the top of the tryptic soy agar plate

with sterile membrane and then incubated for 24 hours at 27℃. Figure 14 shows a

schematic of the experimental setup. Temperature was measured during the experiments

and it remained constant at 28˚C.

Figure 14: Biofouling experimental setup

3.11. Ultra Performance Liquid Chromatography- Mass Spectrometry (UPLC-MS)

PFOA was measured by UPLC coupled electrospray ionization tandem mass spectrometry.

A bench top binary Shimadzu chromatograph (Model: LC-20 AD) and SIL 20 AC

autosampler interfaced with an AB SCIEX mass spectrometer (MS/MS) (Model: 4000 Q

TRAP) were used. In this study, since PFOA was the target analyte, mass labeled

13 perfluoro-n-[1,2,3,4- C4] octanoic acid as surrogate standard (SS), and mass labeled

13 perfluoro-n-[1,2,3,4- C4] heptanoic acid as internal standard (IS) were used. Filtered and

diluted water samples (1.0 mL) were prepared containing 40 ng/L SS and 20 ng/L IS. The

SS spiked samples, continuous calibration verification (CCV), reagent blank and IS-blank were used as quality controls (QC). Target analyte concentrations and QC performance of the method were determined using IS based calibration curves. A gradient elution of mobile phase containing 20 mM ammonium acetate in pure water (A) and pure methanol (B) was used with a Macherey Nagel analytical column EC 125/2 NUCLEODUR C18 gravity packed with 5 µm particle (length 125 x 2 mm ID) at a constant flow rate of 0.4 mL/min.

A 13.51 min gradient with composition of B was started 40% at 0.01 min, 65% at 1 min,

90% at 6 min, 95% at 11.5 min, 40% at 13.51 min with 2 min equilibration time. A volume of 5 µL of standard or samples was injected. Data were collected in negative multiple reaction monitoring (MRM) mode with monitoring of quantitation and qualifier ions for

PFOA, SS and IS. Data acquisition and process were performed using AB Sciex Analyst version 1.4.2 and Multiquant version 3.0 software, respectively. The precursor and product ions monitored were PFOA 412.912 > 368.7, 168.7 m/z; SS 416.946 > 371.9 171.7 m/z;

IS 366.897 > 321.7, 171.6 m/z were obtained. Bold face indicates the quantitation ions.

The PFOA, SS and IS were eluted from column at retention times of 6.57, 6.58, 6.03 min, respectively. Average spiked SS recovery was for 99.2% and average analyte CCV recoveries 105.4%. Limit of detections (LOD) for target analytes were 0.25 ng/mL at S/N=

4. Seven calibration points with linear dynamic range (LDR) were 1.0 - 160 ng/mL with

R2 values of 0.9986. MS was operated with curtain gas 30 psi, negative ESI 4500-volt, temperature 300 oC, and ion sources gas (GS1/GS2) 30 psi.

CHAPTER 4. Self-Cleaning Nanocomposite Membranes with Phosphorene- Based Pore Fillers for Water Treatment This chapter has been published in the following report on an open access journal:

Eke, Joyner, Katherine Elder, and Isabel C. Escobar. "Self-cleaning nanocomposite membranes with phosphorene-based pore fillers for water treatment." Membranes 8, no. 3

(2018): 79.[216]

4.1. Introduction

Nanomaterials with tunable properties show promise for numerous technologies [3, 4, 217,

218] because of their size-dependent electronic structure and controllable physical properties. Two-dimensional nanomaterials are materials that can be isolated as freestanding one atom thick sheets [6]. They are typically generated from bulk-layered crystalline solids [7]. These solids consist of successive layers of covalently bonded atomic layer planes ranging from one to multiple atoms thick, separated successively by van der

Waals gaps [8]. Phosphorene distinguishes itself from other 2-D layered materials by its intrinsic structural anisotropic features [219]. Unlike graphene, phosphorene combines a high carrier mobility with a fundamental band gap [14], which imparts an intrinsic fine- tuning ability [220], thereby providing numerous opportunities for research. Specifically, relevant to the field of membrane science, the band gap of phosphorene provides it with electronic [221] and photocatalytic [179] properties, which could be explored in making reactive membranes that could simultaneously remove and destroy compounds. Using theoretical computational studies, Liang et al. [222] and Zhang et al. [223] studied the performance of self-passivated porous phosphorene membrane in hydrogen purification.

The results showed excellent permeance and significant selectivity for hydrogen over

carbon dioxide, methane, and nitrogen, which suggests that phosphorene shows potential

for hydrogen purification. However, no experimental studies were performed.

Nanocomposite membranes are membranes that consist of polymeric or ceramic materials

and nanomaterials. Nanoparticles can be deposited on the surface or embedded within the

membrane matrix to impart useful functionality, enhance membrane separation, and anti-

fouling properties [224]. Phosphorene exhibits a strong interaction with light, which is

considered highly desirable in photocatalysis applications. With the high toxicity and

corrosive issues encountered with metal-based photocatalysts (oxides, sulfides, and

nitrides of titanium, tungsten, cadmium, and transition-metal dichalcogenides),

phosphorene can act as a metal-free photocatalyst to degrade organic compounds in the feed solution to make reactive and self-cleaning membranes. Through liquid and/or mechanical exfoliation or direct synthesis, two-dimensional materials can be either assembled as a thin active layer on the membrane surface or incorporated into the membrane polymer matrix [225]. The degradation of phosphorene obtained by liquid- phase exfoliation occurs more slowly than that for phosphorene prepared by mechanical

cleavage [34]; therefore, liquid-phase exfoliation of black phosphorus was chosen and was carried out in a basic medium, since this technique produces phosphorene with high water stability and controllable size and layer number [22].

The purpose of this study was, for the first time, to experimentally determine the viability of exfoliated phosphorene to be embedded in a polymer matrix to fabricate self-cleaning membranes. To fabricate membranes, a polymer blend was used to obtain a polymer material with properties intermediate between those of the pure components. The 58

hydrophilic–hydrophobic balance, as well as other properties, such as physical structure

and surface/pore charge of a membrane system, were altered since the membrane was

prepared from a multi-component polymer blend [87]. For this study, the base membrane

dope solution consisted of a blended polymer prepared by dissolving polysulfone (PSf) and

sulfonated poly ether ether ketone (SPEEK) in a (95/5%) ratio into N-methyl pyrrolidone

(NMP). SPEEK is a hydrophilic and negatively charged polymer with low permeability

and mechanical strength; on the other hand, while PSf has good chemical resistance, high

thermal stability, and good mechanical properties, it is hydrophobic and has poor solubility

in solvents. The blend of PSf and SPEEK has been shown to result in a membrane with

higher water permeability and permselectivity as compared to the pure polymers [226].

Using physical mixing between the blended membrane polymer dope and phosphorene,

van der Waals interactions were formed between the constituents, and hence, phosphorene

nanoparticles were incorporated into the dope solution. Methylene blue (MB) was filtered through the membranes under ultraviolet light, and the permeability and selectivity of the membranes were determined. The goal of this study was to determine if the addition of potentially photocatalytic phosphorene to polymeric membranes operated under intermittent UV irradiation would be able to produce self-cleaning membranes, as shown

in Figure 15.

Figure 15: Preparation of a phosphorene-incorporated nanocomposite membrane

4.2. Experimental

4.2.1. Materials

Bulk black phosphorus was purchased from Smart Elements Inc., Vienna, Austria.

Powdered PEEK, N-methyl-2-pyrrolidone (NMP), sodium hydroxide, and concentrated

sulfuric acid (95–98%) were purchased from VWR, Radnor, PA, USA and Polysulfone

(Solvay, Princeton, NJ, USA).

4.2.2. Exfoliation of Phosphorene from Black Phosphorus

The liquid exfoliation of black phosphorous (BP) was carried out using previously

developed methods [22]. Bulk black phosphorus (15 mg) was added to 15 ml of NaOH and

15 ml of NMP solution in a ratio of 1:1. To exfoliate bulk black phosphorus, the mixture 60

was sonicated using an ultrasonicator (P70H, Elma Elmasonic P, Singen, Germany) operated at 37 kHz frequency and 80% power for 4 h. After exfoliation, the solution was centrifuged at 3000 rpm for 10 min and it separated into two phases (exfoliated and non- exfoliated bulk BP), the non-exfoliated bulk BP was then discarded. The supernatant

(exfoliated BP) was centrifuged at 4000 rpm for another 20 min to obtain fewer layers of phosphorene from NMP. The precipitations obtained were redispersed in water and the solutions were rinsed in deionized water for Raman studies. Raman studies were done on a silicon chip.

4.2.3. Membrane Preparation

The blended polymer dope solution was prepared by dissolving PSf and SPEEK (95/5%) into NMP. Exfoliated black phosphorus was added to the solution (0.5% wt./vol) and sealed with parafilm to prevent air bubbles from being trapped inside the solution and affecting the homogeneous mixing of the solvent and the solute. The blended solution was placed on a magnetic stirrer and heated at 65 °C. It was degassed in a sonicator to remove air bubbles for 1 h. The blended solution was spread on a glass plate with a doctor blade at a wet thickness of 0.250 mm and exposed to air for 12 s. A clean glass mirror was used as a surface, which provided optimum hydrophobicity to the membranes and helped the detachment of polymer films during phase inversion [227]. The glass plate and dope solution were immersed in a coagulation bath of deionized water and the membrane was formed via the process of phase inversion. The membranes formed were subsequently washed thoroughly with deionized water to remove residual solvent and kept in deionized water before testing. The thickness of the membrane was maintained at approximately 150

microns. By physical mixing between the blended membrane polymer dope and

phosphorene, phosphorene nanoparticles were incorporated into the dope solution.

Polymers that have similar solubility parameters with solvents are miscible [228], and

closer values typically indicate better compatibility [229]. The solubility parameters of the

polymers used for this experiment were the following: polysulfone, 21.2 (MPa1/2) [230]

and sulfonated polyetheretherketone, 26.2 (MPa1/2) [231] and the solvent, NMP has a

solubility parameter of 22.4 (MPa1/2) [232]. These values indicate that the membrane made

with these polymers–solvent combinations should be stable.

4.2.4. Flux Analysis

Flux analysis was performed in accordance with previously published studies [191] and

will be summarized here. Filtration experiments were performed in batch mode but under

continuous stirring using an Amicon filtration cell (Amicon Stirred Cell 8010–50 ml,

Burlington, MA, USA). The method used to monitor the flux performance of the membrane

was dead-end filtration. To determine flux through the membrane, the time to collect a 2-

ml permeate sample was measured for each feed. Surface area and pressure were kept

constant for the duration of the experiment. The active filtration area was 13.4 cm2 and the pressure was 2.06 bar (30 psi). Flux values were calculated as L/m2h and plotted against

the total time of filtration. Membrane samples were supported with WhatmanTM filter paper

(110 mm). Each membrane was precompacted with deionized (DI) water until a stable flux was reached. Precompaction was followed by filtration of dye solutions of 10 ppm each of methylene blue (MB) in water. The concentrations of the dye were determined using a bio- plate reader and the dye rejection was calculated according to Equation (6) [191]:

R = (1 − (Cp/Cf)) × 100% (6)

where Cp and Cf are solute concentrations in permeate and feed solutions, respectively.

After water filtration, reverse-flow filtration using DI water was performed to remove reversibly attached foulants that were not adsorbed to the membrane, and the filter paper support was changed. The flux recovery of the membrane was measured afterwards

4.2.5. Filtration Experimental Setup

Phosphorene was immobilized into PSf-SPEEK membranes. The resulting membrane was tested for the photo degradation and mineralization of an organic dye, methylene blue

(MB), under near-UV/Vis (Spectroline Model EA-160, Westbury, NY, USA) and in continuous operation mode. To examine the effects under visible light, two similar experiments were set up with the filtration cell, one completely covered by aluminum foil to prevent penetration of sunlight, and irradiated with UV light for 30 min, while the other was uncovered. The wavelength of UV was 365 nm. The permeates were analyzed via a bio-plate reader at 662 nm (Biotek Instruments, Winooski, VT, USA).

4.2.6. Contact Angle Measurement

Contact angle is a measure of the wettability of a surface. Here, a drop shape analyzer

(Kruss DSA100, Matthews, NC, USA) was employed to carry out the contact angle measurement of all the membrane samples. The process for taking a measurement involved adding a small drop of water on the membrane surface and measuring the resultant angle of the droplet to the surface [233]. Hydrophilic materials display lower contact angles as compared to more hydrophobic materials.

4.2.7. Zeta Potential

Zeta (ζ) potential is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle [193]. It is used to determine the surface charge of materials under different pH environments. For this study, an Anton Paar

SurPASS electrokinetic analyzer (Anton Paar, SurPASS, Ashland, VA, USA) in surface analysis mode was used. To ensure the removal of solvents from the membrane surface, membranes were rinsed with DI water before running analysis. The ionic strength of the potassium chloride electrolyte solution used in these measurements was 1.0 mM.

Measurements were done under several pH environments and the pH was adjusted using

0.5 M NaOH and 0.5 M HCl solutions.

4.2.8. Raman Studies

The theory of Raman spectroscopy is discussed elsewhere [29,30], and briefly summarized here from those. When light is scattered from a molecule or crystal, most photons are elastically scattered. The scattered photons have the same energy (frequency) and, therefore, wavelength, as the incident photons. However, a small fraction of light is scattered at optical frequencies different from, and usually lower than, the frequency of the incident photons. The process leading to this inelastic scatter is termed the Raman effect.

Raman scattering can occur with a change in vibrational, rotational, or electronic energy of a molecule. Raman scattering occurs only when the molecule is polarizable. If the scattering is elastic, the process is called Rayleigh scattering. If it is not elastic, the process is called Raman scattering [196, 234]. Raman spectroscopy is a vibrational technique. In an inelastic process, like the Raman scattering, light is scattered and a phonon or normal

mode is created or destroyed [216]. For a vibration to be active in a Raman spectrum, the

vibration must change the polarizability of the molecule. Using the group theory and

character tables, vibrational modes can be assigned to a molecule. Raman spectroscopy has

been widely used to understand the electronic and vibrational properties, as well as their

dependence on the thickness of various 2-D layered materials [200, 201]. The pump

radiation was supplied by a laser operating at a wavelength of 632 nm; the Raman emission

was collected by a 100× objective in a backscattering geometry. A He-Ne laser was used

at a power of 20 mW, but a neutral density filter was done on the sample so the laser spot

on the sample had less than 0.1 mW.

4.2.9. Liquid–Liquid Porometer Studies

A porometer model LLP-11000A (PMI, Ithaca, NY, USA) was used in this study. The

procedure involves a pair of immiscible liquids, of which the liquids used to wet the

membrane, is referred to as the wetting liquid (isopropanol in this case), while the second

liquid (sliwick oil) is used to displace it. By measuring the pressure and the flow through

the membrane, the corresponding pore radius can be calculated using the Cantor Equation

(7) [235] and the contact angle is assumed to be zero:

P = (2γcosɵ/rp) (7)

where P is the pressure, γ is the interfacial tension, θ is the contact angle, and rp is the pore

radius.

4.2.10. Morphological Characterization A FEI Quanta 250 FEG Dual Beam Electron Microscope (FEI, Hillsboro, OR, USA), which has an energy dispersive X-ray spectroscope (EDX) attached to it (Oxford 65

Instruments, X-Max), was used to characterize the samples here. To visualize clearer

images, small samples of the membranes were frozen in liquid nitrogen before cutting.

Cross-section imaging of the membranes was achieved by vertical attachment to a carbon

tape, while surface imaging of the samples was achieved by horizontal attachment. The

surfaces of the samples were sputtered with a thin layer of palladium-gold using a

sputtering device (Emscope SC400, Kent, United Kingdom) and then observed under a scanning electron microscope, and then the EDX analysis was performed on the sample.

4.2.11. Surface Fluorescence Characterization

To determine the level of fouling by MB after each experiment, the membranes were imaged under a fluorescent microscope. Images where recorded on a Zeiss 880 NLO upright confocal microscope (Thornwood, NY, USA) with a 10× air objective. The membranes were sandwiched between microscope slides and wetted with water for smoothing them out. Tiles, showing the full field of over a z-range to cover the slightly non-planar geometry of the membrane, were stitched together in a format of 3 × 3, reflecting a representative cover. Methylene blue was excited with a 633 nm laser and emission was collected over a spectral range of 642 to 759 nm.

4.3. Results and Discussion

Using dynamic light scattering, the average hydrodynamic diameter of the phosphorene nanoparticles after exfoliation was found to average 1.87 nm. To confirm that few-layer

phosphorene was fabricated, thin phosphorene films were first identified using optical

microscopy before being studied under the Raman microscope. Raman spectroscopy was

used to analyze few-layer phosphorene (i.e., between 2–5 layers) after exfoliation. Sample

analysis was performed under ambient conditions. As seen in Figure 16, Raman bands were

−1 −1 −1 1 observed at 463 cm , 436 cm , and 359 cm , assigned to the one out-of-plane mode A g

2 1 2 and two in-plane modes, B2g and A g (A g, B2g, and A g represent vibrational modes) of few-layer phosphorene corresponding to observed values from the literature [236].

Figure 16: Phosphorene characteristic Raman bands

Figure 17 A,B shows the cross-section of the pore structure of SPEEK membranes before and after the addition of phosphorene, respectively, while Figure 17 C,D shows the surface images of both membranes before filtration. By comparing images, it was confirmed that phosphorene was immobilized into the membranes. The phosphorene membranes showed spherical-looking structures present in the pores, which upon analysis by EDX, were confirmed to come from phosphorus. Phosphorene nanoparticles were blended with the dope solution before casting the membrane, and while care was taken to prevent

agglomeration, nanoparticle agglomeration still occurred, and it is believed that the

increase in nanoparticle size after casting was likely due to agglomeration.

(A) (B)

Figure 17: Cross-section SEM analyses of (A) SPEEK membranes and (B) phosphorene- membranes with some of the phosphorene nanoparticles marked in red, and surface SEM analyses of (C) SPEEK membranes (50-micron magnification) and (D) phosphorene- membranes (10-micron magnification) before filtration Figure 18 A,B show the associated EDX spectra for the SPEEK and phosphorene membranes, respectively. From Figure 18 A, SPEEK membranes contained 82% carbon,

14.4% oxygen, 3.6% sulfur, and no detectible phosphorus. On the other hand, the EDX

spectrum of the membranes incorporated with phosphorene (Figure 18 B) show 65.8% carbon, 14.5% oxygen, 16.5% sulfur, and 3.1% phosphorus. Therefore, both Raman and

EDX analyses support the exfoliation of few-layer phosphorene and the subsequent the presence of phosphorene in the membranes, respectively. Since SPEEK has no phosphorus,

all the phosphorus fraction measured was due to the presence of phosphorene on the

membranes, and it amounted to 3.1% phosphorus.

(A)

(B)

Figure 18: A) EDX spectrum of SPEEK membrane showing the presence of carbon, oxygen, and sulfur. (B) EDX spectrum of phosphorene containing SPEEK membrane showing the presence of carbon, oxygen, sulfur, and

phosphorus.

The pore diameter at the maximum pore distribution, i.e., the most prevalent pore size, of the the SPEEK membranes was on average 0.022 microns (with smallest and largest detected

pores being 0.017 and 0.086 microns), while that of the phosphorene membranes averaged

0.0024 microns (with smallest and largest detected pores being 0.0022 and 0.0078

microns), which further indicates the addition of phosphorene accumulating within the

pores, in agreement with Figure 17B, and puts the membranes in the nanofiltration range.

Phosphorene membranes also displayed different pore size distributions, with pore sizes not being as uniform when compared to the baseline SPEEK membranes. This again

showed good agreement with scanning electron microscopy (SEM) images (Figure 17)

since Figure 17 B shows that phosphorene accumulated in some of the pores of the

membranes, which would lead to the formation of smaller, non-uniformly distributed

pores.

SPEEK membranes displayed an average hydrophilicity as measured by contact angle of

48.3° ± 0.67°, while phosphorene-membranes had an average contact angle of 81.5° ±

0.64°. This shows that unmodified membranes were more hydrophilic, while phosphorene

membranes had a more hydrophobic nature that is associated with the presence of the more

hydrophobic phosphorene [237]. The switch from a more hydrophilic to a more

hydrophobic membrane further supports that the chemistry of the membrane had changed,

which was due to the addition of phosphorene. To further characterize changes incurred by

the addition of phosphorene, the surface charge was evaluated, as shown in Figure 19. It

was observed that both SPEEK membranes and phosphorene membranes were negatively

charged in both acidic and basic mediums. At a pH of approximately 6, the zeta potential 70

of SPEEK was −61 ± 4.6 mV while that of the phosphorene membrane was −44 ± 7 mV,

which was possibly due to the phosphorene nanoparticles masking some of the sulfonic

sites (the source of the negative charge of the membranes).

(A) (B) Figure 19: Surface charge vs pH plot of (A) SPEEK membrane and (B) phosphorene- modified membrane.

By employing dead-end filtration, flux studies were carried out on the membranes under

intermittent UV light irradiation. Precompaction, or filtration of pure water, was first

performed to ensure that all solvents used during the membrane fabrication process were

removed from the membranes’ surfaces and pores. As seen in Figure 20A,B, the average

initial pure water flux values for SPEEK and phosphorene membranes were 67 ± 20.0 LMH and 107 ± 33.6 LMH, and the flux values at the end of precompaction were 37 ± 17.8 and

82 ± 24.9 LMH, respectively. Reasons for the high standard deviation include the fact that membrane samples were fabricated in laboratory-scale batch processes, and reaction completion was determined via reaction time; therefore, each batch could have slight differences when compared to others. Furthermore, small pieces of membrane were cut out

for each experiment, having an area of 13.4 cm2. Both membranes obtained MB rejections

of approximately 89%. While average values were different, standard deviations show that

flux values of SPEEK and phosphorene membranes were not different from each other.

The likely reason for the higher flux values might have been because phosphorene membranes were more sponge-like, and hence more porous, as compared to SPEEK

membranes, which was evident from the SEM images (Figure 17).

After precompaction was completed, MB solutions were filtered through the membranes, and after filtration, membrane cleaning was simulated via reverse-flow filtration using pure water to investigate the potential for cleaning. Initial MB solution filtration displayed flux

values of 42 ± 30.1 and 68 ± 20.3 LMH for SPEEK and phosphorene membranes,

respectively, while final flux values were 29 ± 16.9 and 30 ± 2.7 LMH for SPEEK and

phosphorene membranes, respectively. The decrease in flux values during filtration

showed that for both SPEEK and phosphorene, MB accumulated on the surface of the

membranes to foul them. To measure the ability of phosphorene’s photocatalytic properties

in self-cleaning the membranes under UV irradiation, the recovered fluxes were monitored.

It was determined that for the SPEEK and phosphorene membranes, the recovered flux

values were 17 ± 6.3 (or 45% of the initial pure water flux) and 70 ± 5.8 LMH (or 85% of

the pure water initial flux, or a flux value similar to that at the start of MB filtration). Only

after UV irradiation was the flux of phosphorene membranes higher and different as

compared to SPEEK membranes.

(A)

(B) Figure 20: (A) Flux analyses of SPEEK membrane under UV irradiation at a constant pressure of 2.06 bar (B) Flux analysis of the phosphorene-modified membrane under UV irradiation at a constant pressure of 2.06 bar

Table 1 summarizes the flux values obtained. Experiments were replicated three times. It was hypothesized that the membranes could become self-cleaning under the intermittent application of UV irradiation. This was verified by performing experiments using phosphorene membranes operated with and without UV irradiation. Under visible light

(i.e., without UV irradiation), the recovered flux after reverse-flow filtration with pure water using phosphorene membranes was 35% of the initial flux at the start of MB filtration

(i.e., the initial flux was 71 LMH and the recovered flux was 25 LMH). On the other hand,

the phosphorene membrane operated under UV irradiation showed a full recovery of flux

after reverse-flow filtration using pure water (i.e., the initial flux was 68 LMH and the

recovered flux was 70 LMH). With the only variable being the presence of UV irradiation,

and both membranes showing similar MB rejection at approximately 89%, it is

hypothesized that the MB accumulated on the surface of the membrane was potentially

destroyed, which would make the membrane self-cleaning.

Table 1: Flux values of phosphorene membranes operated under UV irradiation and without UV irradiation

Phosphorene Membranes Phosphorene Membranes Flux Type Operated without UV Operated with UV Flux (LMH) St. dev Flux (LMH) St. dev PWF Initial 56 2.6 107 33.6 PWF Final 74 7.1 82 24.9 MB Initial 71 12.5 68.1 20.3 MB Final 57 10.8 31 2.7 Recovered 25 5.3 70 5.8

Figure 21A,B show images of the MB stained membranes to evaluate the amount of MB

that accumulated after reverse-flow pure water filtration, which provides a qualitative

measure of the amount of MB that remained intact and irreversibly attached to the

membrane. SPEEK membranes showed full coverage of MB, while phosphorene membranes did not show a uniform coverage of methylene blue under fluorescence. The

SPEEK membranes had a coverage four times higher than that observed with the phosphorene membranes. This decrease was possibly due to the destruction of MB, and it

agreed with the higher flux recovery values obtained when using phosphorene membranes.

It is proposed that because phosphorene has a band gap that can be tuned sufficiently for

photon absorption in the ultraviolet region, photocatalysis of the dye may have occurred

under UV irradiation. This made the phosphorene membranes self-cleaning, as observed

by a higher flux recovery.

(A) (B) Figure 21: (A) Fluorescent image of SPEEK membrane after the reverse-flow filtration. (B) Fluorescent image of phosphorene-modified SPEEK membrane after the reverse-flow filtration.

4.4 Conclusions

For the first time, nanocomposite membranes were fabricated using phosphorene. This

opens the field to a new class of potentially reactive membranes, or at the least, easier to

clean membranes. Due to phosphorene’s properties, these membranes have the potential to

be used for multiple purposes, such as compound destruction, self-cleaning, biofilm formation prevention, etc. Membrane separations of the future will not favor static membranes, i.e., membranes that only serve the function of rejecting compounds, since accumulated and potentially hazardous compounds on the surface will be released on backwash/cleaning water to make that hazardous and make the membranes hazardous at the time of disposal. Hence, dynamic self-cleaning membranes that can simultaneously remove compounds and destroy them provide the field with an alternative. There are numerous reactive membranes in existence, but phosphorene brings tunable properties that open a new field for research.

CHAPTER 5. Nanohybrid Membrane Synthesis with Phosphorene Nanoparticles: a Study of the Addition, Stability and Toxicity This chapter has been published in the following report and adapted with permission from:

Eke, Joyner, Philip Alexander Mills, Jacob Ryan Page, Garrison P. Wright, Olga V.

Tsyusko, and Isabel C. Escobar. "Nanohybrid membrane synthesis with phosphorene nanoparticles: a study of the addition, stability and toxicity." Polymers 12, no. 7 (2020):

1555.[238]

5.1. Introduction

Membranes play a crucial role in the purification of water and wastewater [239]. Within the broad range of membrane materials, polymeric membranes are attractive because they exhibit high chemical and mechanical resistance [240] and offer a wide range of pore sizes; however, polymeric membranes are plagued by fouling, which is a problem that has hindered fast adaptation of membranes in relevant fields. Fouling is the buildup of unwanted materials on the membrane surface and within the pore structure. Fouling materials are grouped under three generic headings, namely organic foulants (proteins, humic and other organic compounds), inorganic foulants (mineral salts, crystallized salts, oxides and hydroxides and colloidal particles), and biological foulants (biofilm formation by microorganisms) [241]. Fouling inhibits membrane performance as measured by permeability and selectivity, increases membrane maintenance costs, and ultimately shortens the lifespan of the membrane [242]. Membranes can be functionalized with reactive nanomaterials to improve their fouling resistance properties [243].

Dynamic/reactive membranes can mitigate fouling by the generation of reactive oxygen

species, which oxidize foulants present on the membranes [216] thus leading to a self-

cleaning phenomenon.

Two-dimensional materials are being increasingly researched as membrane additives since

they create ultrathin separation layers within the membrane that are highly selective for

molecules and ions [225]. Two-dimensional nanomaterials are materials that can be

isolated as freestanding one-atom-thick sheets [6]. One of such two-dimensional materials

is phosphorene, which was discovered in 2014 [24], and was found to exhibit improved

optical properties; it displays optical absorption peaks at 1.2 eV and absorbance spectrum

across both the IR (infrared) and visible light spectra [244]. These optical properties can

be explored in photocatalysis, hence, it can be considered to be a potential metal-free

photocatalyst [245]. In the study done by Yang et al, by applying density functional theory

calculations [246], phosphorene was shown to display photocatalytic hydrogen production

properties. Phosphorene is a single layer, two-dimensional layered material, exfoliated form of black phosphorus (BP). Unique properties of phosphorene include its highly

anisotropic electric conductance and its strong interaction with light. Phosphorene

distinguishes itself from other 2D layered materials by its intrinsic structural anisotropic

features [247]. Unlike graphene, phosphorene combines a high carrier mobility with a

fundamental band gap [14] which imparts an intrinsic fine-tuning ability [220], thereby providing numerous opportunities for research. The main issue with phosphorene is the fast degradation under ambient conditions because of the generation of reactive oxygen species. Research however has shown that incorporating phosphorene into polymers preserves the structure and properties of phosphorene [248, 249]

Specifically relevant to the field of liquid separations using membranes, the band gap of phosphorene provides it with electronic [221] and photocatalytic [179] properties, which could be explored in making responsive membranes that could simultaneously remove and destroy organic compounds. Phosphorene has recently been used as a catalyst for arsenic removal [250] and as a photocatalyst for dye degradation [216]. However, a key issue with phosphorene is instability when exposed to air, which causes it to degrade into phosphorus oxides that may affect its chemical and physical properties [251]. Several studies have focused on addressing this issue, such as Ryder et al. produced phosphorene nanoparticles that were stable in ambient conditions for three weeks by chemically modifying exfoliated black phosphorus with an aryl diazonium molecule which formed covalent phosphorus- carbon bonds and increased their stability [252]. Recently, Qiu et al. synthesized phosphorene, which exhibited stability when exposed to ambient conditions for four months by crosslinking black phosphorus with polyphosphazene [253].

Integrating nanoparticles within polymeric membrane matrices could lead to increases in their selectivity, thermal stability, permeability as well as altering their water affinity characteristics [254]. Nanoparticles can be prepared using physical processes that utilize a top-down technique (breaking down the bulk material into nanoparticles), or chemical processes which utilize bottom-up techniques (typically employ chemical reactions to assemble atoms together) [255]. Several techniques for incorporating these nanoparticles into membranes include layer by layer assembly, chemical grafting, self-assembly and physical deposition, amongst others [108]. Common problems of aggregation and/or leaching of the nanoparticles may occur irrespective of the technique used for incorporating them into the membranes. Nanoparticle agglomeration occurs as a result of the very

attractive forces between the nanoparticles, such as van der Waals and electrostatic forces

[256]. While converting bulk crystalline solids into spherical nanoparticles, there is an energy loss associated with the deformation of the particles. At the point of contact between two nanoparticles, an adhesive grain boundary is formed that is thermodynamically stable.

The energy at the free surface of these nanoparticles is two times higher than the energy at the grain boundary. As a result, whenever two nanoparticles come in contact, there is always an energy gain, hence agglomeration occurs [257]. To prevent agglomeration, an opposite repulsive force is required [255]. When phosphorene is made by exfoliating bulk crystalline black phosphorus, agglomeration may occur.

Leaching of nanoparticles from polymer media is a common phenomenon because, stabilizing nanoparticles in aquatic environments is intricate as a result of the Brownian diffusion that largely controls particle movements [258]. Other interactions that govern nanoparticle stability include steric, hydration and magnetic forces. Coagulation of nanoparticles in a solvent media can be prevented by stabilizing with a polymer because they can induce steric stabilization in the particles [259]. Although with a weak solvent, the van der Waal interactions can dominate and cause the polymer layer to collapse leading to coagulation [260]. Among factors governing how the polymer interacts with the nanoparticle are the technique used in coating the nanoparticle with the polymer

(adsorption vs grafting), the level of coverage and nature of the polymer[261].

Phosphorene is a metal-free photocatalyst and provides advantages over application of toxic metal-based photocatalysts such as oxides, sulfides and nitrides of titanium, tungsten, cadmium, and transition-metal dichalcogenides. Several studies have examined in vitro and in vivo toxicity of phosphorene and demonstrated that it can cause toxicity [262, 263]. 80

The observed cytotoxicity from phosphorene in one of the studies was lower than that of

graphene [264]. Mice exposed to black phosphorus quantum dots after showing signs of oxidative stress were able to recover from the exposure [265]. There is evidence that

phosphorene nanosheets can penetrate cell membranes and interact with phospholipid

layers, and the degree of these interactions, as well as resulting toxicity, are determined by

the size and concentrations of phosphorene and the cell types[266] . It is still unknown,

however, whether phosphorene embedded into polymeric membranes will be released at

the concentrations that could cause toxicity. In this study we utilized a powerful model

organism, a nematode Caenorhabditis elegans to test for in vivo toxicity of phosphorene.

Due to their short generation time, ease of maintenance and prolific reproduction C.

elegans has been extensively used as a model organism for a toxicity testing of various

contaminants including nanomaterials [267, 268]. In addition, its genome is fully

sequenced, annotated, and functional genomic tools are readily available for examining

toxicity mechanisms.

As more researchers turn to two dimensional materials for membrane modifications, the

need for a 2D material that inherently allows fine tuning towards membrane enhancement

is pertinent. Graphene has no band gap and other 2D transitional metal dichalcogenides

(TMDs) possess band gaps only as monolayers [269]. Phosphorene has direct band gaps in

all its three forms, bulk, monolayer, and few layers [269]. Phosphorene has also been

studied for its electrocatalytic properties, which research shows outperforms ruthenium (iv)

oxide and Co3O4 /N-graphene [270]. Currently, while a large bulk of experimental research

efforts has focused towards producing air stable phosphorene [269-272], there is limited

information on the incorporation of phosphorene in membranes as well as a thorough

understanding of its physicochemical properties when utilized as a membrane additive. In

a previous study [216], the photocatalytic properties of phosphorene-based membranes were examined; on the other hand, in this study, the effects of phosphorene on the morphological structure of the polymeric blend along with the evolution of the modifications were investigated. Furthermore, we discuss its stability under several pH environments as well as study biological effects of phosphorene-based membrane permeates on a nematode.

The overarching goal is to develop stable and non-toxic phosphorene polymeric membranes. To achieve this goal the prepared phosphorene membranes were thoroughly characterized with respect to their structural and morphological characteristics, permeability, and selectivity, as well as toxicity. Our specific objectives were to 1) incorporate phosphorene into a polymer blend of polysulfone (PSf) and sulfonated poly ether ether ketone (SPEEK) to cast ultrafiltration membranes; 2) examine stability of phosphorene in acidic, basic and neutral environments; 3) determine the level of adhesion of phosphorene to the membranes via leaching experiments with a closed cross flow filtration; 4) examine toxicity of free phosphorene and permeates of phosphorene membranes to C. elegans.

5.2. Materials and Methods

5.2.1. Materials To produce few-layers phosphorene, bulk black phosphorus was purchased from Smart

Elements, Vienna, Austria. Polysulfone (PSf), poly ether ether ketone (PEEK), N-methyl pyrrolidone (NMP), used to prepare the dope solution for ultrafiltration membranes, were

purchased from VWR, Radnor, USA. Methylene blue was purchased from VWR, Radnor,

USA. Sodium hydroxide (NaOH), bovine serum albumin (BSA), sodium chloride (NaCl),

concentrated sulfuric acid, phenolphthalein indicator and citric acid were also purchased

from VWR, Radnor, USA. The cross flow cell was designed in the laboratory. The

ultrasonicator model P70H was purchased from Elmasonic P, Singen, Germany. A dead-

end cell, Amicon Stirred Cell 8010–50 mL, was purchased from EMD Millipore,

Burlington, MA, USA. Total organic carbon analyzer TOC- 5000A was purchased from

Thermo Scientific, Waltham, MA.

5.2.2. Sulfonation of PEEK and Determination of Degree of Sulfonation

The recipe for making the SPEEK polymer dope has been previously reported in the literature [216], so it is briefly discussed here. To synthesize sulfonated poly ether ether ketone, PEEK pellets were dried in the oven at a temperature of 60˚ C overnight and then dissolved in a 98% concentrated sulfuric acid solution for three days at room temperature.

After dissolution, it was gradually added into an ice water bath under mechanical agitation to precipitate SPEEK (sulfonated poly ether ether ketone) pellets. SPEEK was thoroughly washed in deionized water until a pH of 7 was attained. Then it was dried in the oven at

60˚ C and stored for use.

The degree of sulfonation (DS) is the content of hydrogen sulphite present after all possible substitution for hydrogen sulphite has occurred on all points in the substitution site [184].

For SPEEK, sulfonation usually happens on the phenyl ring located between the two ether groups of the PEEK repeat unit [185]. SPEEK with a high degree of sulfonation (DS) has a relatively low chemical stability [186]. Hence, it is necessary to calculate DS. To

quantitatively determine the DS, the 1H NMR spectra of SPEEK in a deuterated solvent, dimethyl sulfoxide (DMSO-d6) was carried out. At a frequency of 400MHz, a Bruker

(Billerica, MA, USA) Avance NEO spectrometer equipped with a Smart Probe was utilized for this experiment. 5wt% of SPEEK was dissolved in DMSO-d6. The internal standard used was DMSO at 2.5 mg/L. The assignment of the peak signals was from literature [187].

The presence of –SO3H group after substitution results in a down field shift of the nearest neighboring proton (H10). Using equation 1, the DS was estimated from the ratio between the peak area of H10 and the total integrated peak area of all the remaining aromatic protons

(Hx, where x =1,2,3,4,5,6,7,8,9,11).

( ) = = ( 0 ≤ y ≤ 1)[184] (1)

𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂 𝒐𝒐𝒐𝒐 𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 𝑯𝑯𝟏𝟏𝟏𝟏 𝒚𝒚 𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨 𝒐𝒐𝒐𝒐 𝑯𝑯𝟏𝟏𝟏𝟏 ∑ 𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷 𝒂𝒂𝒂𝒂 𝒂𝒂𝒂𝒂 𝒐𝒐𝒐𝒐 𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 𝟏𝟏𝟏𝟏−𝟐𝟐𝟐𝟐 ∑ 𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨 𝒐𝒐𝒐𝒐 𝑯𝑯𝑿𝑿 5.2.3. Fourier-Transform Infrared Spectroscopy (FTIR)

FTIR is commonly used in the study, identification, degradation and characterization of polymeric structures [203]. Molecules can absorb light in the infrared region that usually translates into changes in the vibrational frequency [204]. Apart from diatomic elemental gases, all compounds exhibit infrared spectra and can be analyzed qualitatively by their distinctive infrared absorption [204]. Functional groups possess characteristic infrared absorption bands that are synonymous to the stretching, contracting, and bending vibrations of the functional groups. These vibrations are expected within specific regions on the spectra and are influenced by the kind of chemical bonds present in the functional group, as well as the atoms which make up the group [205]. The infrared region of the spectra is divided into three basic regions which are the near-IR, mid-IR, and far-IR. The mid-IR

which falls under wavelength numbers spanning from 400 up to 4000 cm-1 is where most chemical molecules absorb frequencies and exhibit vibrations [206].

5.2.4. Exfoliation of Bulk Black Phosphorus

To produce few-layer phosphorene, the method described by Guo et al [22] and Eke et al

[216] was utilized. Briefly, equal volumes of NMP and NaOH were mixed and degassed on an ultrasonicator (P70H, Elma Elmasonic P, Singen, Germany) for 5 min. 300 mg of bulk black phosphorus was suspended in this mixture and sonicated for 5 hrs. at a frequency of 37 KHz and a power of 80%. The temperature was kept constant throughout the experiment at 30 ˚C. The solution was centrifuged at 4000rpm for 23 mins. The supernatant was used for the experiment.

5.2.5. Transmission Electron Microscopy (TEM) and HAADF-STEM

Exfoliated phosphorene samples were prepared and added dropwise onto a carbon film on a copper grid (Lacey carbon film, 300 Mesh Cu, TED Pella Inc.). The lacey carbon film was then left in a hood overnight to completely dry the solvent. High-resolution transmission electron microscopy (HR-TEM) was performed on a FEI Talos F200X instrument operated at an accelerating voltage of 200 kV and with a point-to-point resolution of 0.1 nm. The TEM images were obtained at typical magnifications of 100 K to 1.05 M. Velox digital micrograph software was used to analyze the samples and Image

J was used to estimate nanoparticle size. Scanning transmission electron microscopy

(STEM) was performed on the same instrument (FEI Talos F200X, using a high angle annular dark field Detector (HAADF) at 200kV. HAADF-STEM image intensity is reported to be proportional to square of the atomic number, so heavy atoms are observed

brighter. The phosphorene nanoparticle composition and element distribution were

determined via FEI super energy-dispersive X-ray spectroscopy (EDX) system.

5.2.6. Optical Profilometer

The surface morphology of membranes influence the fouling pattern, membrane permeability, as well as the solute rejection of the membrane[207]. Studies have shown

that smoother surfaces tend to exhibit lower rejection and higher flux values, whereas,

rougher surfaces exhibit higher rejection and lower flux values [208]. Atomic force

microscopy (AFM) is the most common technique used for characterization of membrane

surface roughness because of ease of use and functionality in different environments [209]

but a major drawback is the limitation on scan surface area. Given that surface roughness

is a function of scan size, a small scan area may be misrepresentative of the true overall

surface roughness [210]. Optical interferometry on the other hand, provides roughness

information over a larger scan size and thus more accurate information can be deduced on

the membrane surface roughness [209]. Optical profilometers are used to evaluate height

variations on surfaces hence information on the surface roughness of the surface can be

obtained. They are interference microscopes that utilize the wave properties of light to

compare the optical path difference between a test surface and a reference surface. Surfaces

can be characterized quickly and precisely to determine surface roughness, critical

dimensions, and any additional topographical features. Measurements made are usually

nondestructive and do not require sample preparation. The Zygo New View 7000 optical

profilometer (Zygo Corporation, Middlefield CT, USA) was used to characterize the

surface of the phosphorene modified membrane as well as the unmodified membrane. The

scan length was 65 µm bipolar (20 secs) and the magnification of the objective lens was

50x. Two dimensional and three-dimensional images were obtained for analysis.

5.2.7. Electrokinetic Potential Measurement

The zeta potential provides information on the surface charge of the membrane surface. An

Anton Paar SurPASS electrokinetic analyzer (Anton Paar, SurPASS, Ashland, VA, USA) was used to determine the zeta potential of the membrane. The electro kinetic potential, commonly referred to as the zeta potential is the potential at the shear plane of a moving colloid particle under an electric field. It describes the potential difference present between the electric double layer of the particles in motion and the stationary layer of dispersant surrounding these particles at the slipping plane [273]. Certain factors control the observed value for zeta potential which include pH, positive in acidic environments and negative in basic environments [274], ionic strength, the higher the ionic strength the lower the zeta potential [273], concentration, dilute solutions have a higher zeta potential [275].

5.2.8. Contact Angle Measurement

The water interaction parameter of a membrane surface plays a key role in water permeability and fouling [276]. For a drop of liquid on a horizontal flat surface, the contact angle is the angle between the juncture of the solid-liquid boundary and the vapor-liquid boundary [277]. When the contact angle of a surface is less than 90° it implies that the surface is a high level of wettability and hydrophilic, while surfaces with contact angles greater than 90° indicates a low amount of wettability and hydrophobicity. For this study, a drop shape analyzer (Kruss DSA100, Matthews, NC, USA) was used to obtain contact angle measurements on all the membrane samples.

5.2.9. Leaching Studies

The stability of static phosphorene within the pores of the membrane was examined using

a cross flow cell in recycle mode. The feed solution, deionized water, was stirred at a rate

of 200 rpm. The phosphorene-imbedded membrane was left in continuous contact with the

deionized water flowing through the cell for fifteen days. Samples were taken daily from

the beaker and tested for presence of phosphorus using an inductively coupled plasma

atomic emission spectroscopy (ICP-OES). During the membrane formation process via

phase inversion in a water bath, samples of the remnant water-solvent mixture were

obtained and tested for phosphorene. Furthermore, the stability of the phosphorene

membranes at various pH levels was tested at room temperature. For the stability studies, concentrations of phosphorene in the dope solutions were 650, 800 and 1000 mg/L.

Phosphorene membranes with an area of 100 cm2 were left in 100 ml of citric acid at pH

4, sodium hydroxide at pH 13, and deionized water at pH 7, respectively for 72 hrs. and

samples were collected and analyzed for phosphorus using the ICP-OES. The detection

limit was 60ppb.

5.2.10. Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) Study

A Varian Vista Pro CCD simultaneous ICP-OES was used to determine the concentration

of phosphorus in samples. The power used was 1.2kW, plasma flow rate of 15 L/min,

auxiliary flowrate of 1.5 L/min, nebulizer flowrate of 0.9 L/min, the replicate read time

was 35 s and the instrument stabilization delay was 20s. Samples were acidified to a pH

<5.5. A 25-ppb analytical detection limit was established with phosphorus calibration

standards prepared in 1% HNO3. Standard curve correlations maintained a correlation

coefficient > 0.995. Sample measurements were read in triplicate. Quality control measures

included a diluent blank, standard control, and yttrium internal standard measurements with

each sample reading. The ICP-OES was also utilized to measure phosphorous concentrations in free phosphorene exposure solutions used in toxicity testing (described

below) as well as in permeates generated by filtering media through phosphorene

membrane.

5.2.11. Morphological Characterization of Membranes using X-ray photoelectron

spectroscopy (XPS) and Scanning Electron Microscope (SEM)

XPS characterization of phosphorene membranes was performed using a Thermo

Scientific K-Alpha XPS apparatus equipped with an Al K (1486.6 eV) source (pass energy

of 20 eV). Phosphorus, carbon, oxygen, and sulfur peaks were fitted using Thermo

Scientific™ Avantage Software. The X-ray source had an emission current of 12 mA and

the acceleration voltage was 10 kV. The spectra measurement was done at a 90o emission

angle. The electron energy analyzer operates in FAT mode (Fixed Analyzer

Transmission), with a constant pass energy of 50 eV for survey (wide) scans and 20 eV for

high resolution scans. The overall resolution of this XPS was about 1.1 eV. Furthermore,

a depth profile scan for phosphorus was done to confirm presence of phosphorus on the

surface of the membrane and within the pores of the membrane.

For the SEM characterization, the membranes were first immersed and ruptured in liquid

nitrogen to obtain a fractured surface with minimal deformation (stretching and tearing).

The resulting fracture, cross-section surfaces were then imaged in a scanning electron

microscope (SEM, Quanta FEG 250, FEI/ThermoFisher Scientific) without conductive

coating

5.2.12. Membrane Synthesis

Optimal materials for membranes should have a blend of high permeability and selectivity,

excellent mechanical strength, great film-forming properties, and chemical and thermal

stability[278]. Finding a polymer with all these attributes may be difficult and hence it is much easier to use polymer blends that can combine together to achieve these characteristics [279]. To make the membrane used for this experiment, a blend of polymers was utilized. PSf has a high thermal and chemical stability, but poor solubility in solvents and hydrophobic, while sulfonated poly ether ether ketone is hydrophilic, but has poor permeability. A blend of the two polymers gives rise to a membrane with high permselectivity and a superior permeability for water [226]. The dope solution consisted

of a (95/5%) ratio of PSf and SPEEK, and 0.5 wt.% of exfoliated phosphorene in NMP.

During the phase inversion process, some loss of phosphorene may have occurred, but this

was unnoticeable. The remnant coagulant bath solution was tested after casting for

phosphorus which was below the detection limit of 50ng/mL. 0.5% w/v of phosphorene

was used (5 mg/mL) during the fabrication of the membrane and since no loss was detected;

therefore, the theoretical percentage of phosphorene in the membrane was 0.5% w/v. Since

nanoparticles can change the morphological structure of membranes by acting as pore

formers, keeping the concentration to a low 0.5 wt.% helped balance the trade-off of their

positive impact on their negative impacts on the membrane [280, 281].The solubility

parameter for the blend polymer mixture and solvent were very close, which further

indicated better compatibility [229] because it leads to a smaller heat of mixing hence

increasing the possibility of a negative Gibbs free energy favoring a stable solution

mixing[282]. SPEEK has a solubility parameter of 26.1 MPa1/2–26.4 MPa1/2 [283, 284] .

Polysulfone has a solubility parameter of 23.7 MPa1/2 [285, 286] and NMP of 23.1 MPa1/2

[286, 287].. Using physical mixing between the blended membrane polymer dope and

phosphorene, Van der Waals interactions were formed between the constituents, and hence, phosphorene nanoparticles were incorporated into the dope solution. The membranes were cast using a doctor’s blade via the non-solvent induced phase separation technique. Figure

22 highlights the major step involved for the fabrication technique. The membranes were stored in deionized water overnight to further eliminate residual solvents.

Figure 22: Fabrication of blend polymeric membrane

5.2.13. Flux Analysis To study the flux performance of the membrane, a 50-ml dead-end filtration cell was used under continuous stirring in a batch mode. A Whatman filter paper (110 mm) was used as a support for the membranes during the experiment. The filtration was done under a constant pressure of 2.06 bar at room temperature. The time for 2 mL of solution to pass

through membranes with an area of 13.4 cm2 was recorded, and the flux, J, was calculated using this equation 2

J = (2) 𝑽𝑽 where V is the𝑨𝑨𝑨𝑨 volume𝑨𝑨 of solution through the membrane in L, and A is the active filtration

area of the membrane cell in m2, and t is the permeation time. Precompaction using

deionized water was done before the filtration of bovine serum albumin (BSA) feed

solution. This was repeated 10 times and then followed by a reverse-flow filtration of deionized water to simulate cleaning to eliminate foulants and determine flux recovery of

the membrane. Using equation 3, the protein rejection of the membrane was calculated.

R = (1 − (Cp/Cf)) × 100% (3)

Where Cp is the protein concentration in the permeate and Cf is the protein concentration

in the feed.

In addition to BSA, 10mg/L of an organic dye, methylene blue (MB), was also filtered

through the membranes and exposed to visible light and ultraviolet light (Spectroline

Model EA-160, Westbury, NY, USA) at a wavelength of 365 nm for 30 mins and visible

light and the membranes were examined under a fluorescent microscope (Zeiss 880 NLO,

Thornwood, NY,USA). The fluorescent intensity was analyzed using ImageJ to evaluate

the percentage coverage of methylene blue on the surface.

5.2.14. Toxicity Testing

For toxicity testing phosphorene was transferred from solvent into DI water for triple

washing. The washing steps required centrifugation at 12,000 g for 20 min, removal of

supernatant leaving phosphorene pellet intact on the bottom of the tube and replenishing 92

with DI water. After third wash, the exposure medium was added. Two media used for the

exposures were 50% K-Medium (31.68 mM KCl and 51.37 mM NaCl) and Moderately

Hard Reconstituted Water (MHRW; KCl 4 mg/L, MgSO4 60 mg/L , CaSO4 60 mg/L,

24-well tissue culture plates were used for exposures with 1 mL of the solution and 10 (±1) nematodes per well, with 4 replicates per concentration. Mortality was scored after 24 h.

The testing for all concentrations was conducted in two independent experiments. For reproduction, eggs were hatched on K-agar plates with E. coli OP50 bacterial lawn, and after 24 h the nematodes at F2 stage were placed into the exposure solutions for 24 h. In each treatment, the nematodes were exposed to four sub-lethal concentrations of

Phosphorene in 50 K-Media or MHRW. The exposures were conducted in the presence of bacterial food, E. coli OP50 at OD600=1 and 10 ul per ml of exposure solution. After

exposures individual nematodes were placed on K-agar plates containing E. coli OP50 and allowed to reproduce. The adults were transferred to the new K-agar plates every 24 h up to 72 h. The offspring that remained on the plate were allowed to hatch and grow for 24 h and after that were stained with Rose Bengal (0.5 g/L) and heated at 55 °C for 50 min. The stained offspring were counted under microscope. The mortality testing were also

conducted with 1, 3, and 5 order of permeates generated after filtering K-medium or

MHRW through phosphorene membrane.

5.3. Results and Discussions

5.3.1. Degree of Sulfonation and Membrane Fabrication

In previous studies, the fabrication of SPEEK membranes along with the incorporation of phosphorene has been discussed [216]. As previously stated, the degree of sulfonation

(DS) is the content of hydrogen sulphite present after all possible substitution for hydrogen sulphite has occurred on all points in the substitution site [184], and SPEEK with a high

DS has a relatively low mechanical stability [186]. As seen in Figure 23, the peak from H10 was a doublet (two close peaks) at 7.5 ppm. The peaks from other protons far away from the carbonyl group, H1,2,7,8,9,11 was noticed at 7.0-7.3 ppm and the remaining peaks at 7.8-

8 ppm. From the 1H NMR, the degree of sulfonation was measured by presetting the integration value of the distinct signal to 1.00 and then obtaining the integration values of the remaining signals from the spectra. These numbers were inserted into equation 1 and the value obtained was 0.77. This means that the chances for SPEEK leaching out of the blend polymer membrane of PSf and SPEEK was low at room temperature since for

SPEEK to dissolve out of the blend, the DS has to be greater than 0.99[288]. Hence, the

SPEEK membranes were considered chemically stable at room temperature.

Figure 23: 1H NMR spectrum of SPEEK in dimethyl sulfoxide

A degree of sulfonation of 0.77 verified that the membranes would not solubilize during

filtration and further supported the recipe used here. Therefore, as previously stated, the

base membrane dope solution consisted of a blended polymer prepared by dissolving PSf

and SPEEK in a 95%:5% ratio, respectively, in NMP. Using physical mixing between the

blended membrane polymer dope and phosphorene, Van der Waals interactions were

formed between the constituents, and hence, phosphorene nanoparticles were incorporated

into the dope solution.

5.3.2. Structural Membrane Polymer Evolution

To verify the blending of PSf with SPEEK and determine if phosphorene led to alterations

in the base polymeric backbone of the membranes, FTIR was performed. Figure 24 shows the FTIR bands at 400-4000 cm-1 of both unmodified and phosphorene membranes.

Polysulfone displays characteristic bands at 1487 cm−1 and 1586 cm−1 [289] which are due

to the stretching vibration of the C=C aromatic ring. Similar bands were observed for both 95

membranes, showing distinctive bands 1487 cm−1 and 1586 cm−1 that verify the presence of PSf Furthermore, the presence of SPEEK was verified by characteristic broad bands at

−1 −1 3450 cm from the hydroxyl group vibrations of SO3H [290], 1230 cm assigned to the vibrations from —O=S=O—groups in SPEEK [290]. Table 2 shows the assignment of bands at different wavelengths. The region of 400-1800 cm-1 was deconvoluted in Figure

25 to determine if there were any band changes. A difference was at 1082 cm-1, associated

3- with the PO4 group from the possible formation of some phosphate associated with the

3- -1 phosphorene addition. PO4 groups form absorption bands at 560-600 cm and at 1000 –

1100 cm-1 [291].

Figure 24: FTIR spectra of phosphorene and SPEEK: PSf membranes over the region 400-4000 cm-1

Figure 25: FTIR spectra of phosphorene and SPEEK: PSf membranes over the region 400-1800 cm-1

Table 2: Assignment of FTIR bands at different wavelength Number Wavelength number(cm-1) Functional group 1 1230 —O=S=O— 2 1487 C=C 3 1586 C=C 4 3450 OH

5.3.3. TEM Analysis

To understand the effect of water on the nanoparticle size, TEM images were obtained.

From Figure 26, it is observed that 2D phosphorene formed distinct spherical nanoparticles in NMP; however, in water, the spherical nanoparticles agglomerated into clusters. pH has

a large effect on nanoparticle agglomerate size [292]. Nanoparticle systems comprise of the nanoparticle and the suspension medium and the flux of hydrogen ions within the system controls agglomeration [292]. At pH levels close to the isoelectronic point of the nanoparticle, agglomeration is promoted. The isoelectronic point for phosphorene is 3.

When phosphorene is suspended in NMP, the sodium hydroxide added during the exfoliation step led the system to become more basic, and hence the agglomeration effect was reduced; on the other hand, when the nanoparticles were rinsed in water, the system became more acidic because of the formation of some phosphoric acid and so agglomeration was favored. Observed nanoparticle size after exfoliation averaged about 5

± 0.3 nm in NMP. However, if the solvent used were changed from NMP to water, the nanoparticle size was observed to increase to an average of 2± 0.9 microns. This occurred likely due to the tendency of the nanoparticles remain discrete in NMP, while agglomerating in water.

(A) (B)

Figure 26: TEM images of 2D phosphorene in different solvents (A) NMP and (B) water

5.3.4. Morphological Characterization of Membranes

Results from the optical profilometer indicated that the SPEEK: PSf membranes had

smoother surfaces than those of the phosphorene membranes. Although the conventional

method of quantifying roughness involves reporting the line roughness parameters, average line roughness (Ra), root mean square line roughness (Rq), and the mean depth of line roughness (Rz) [293], reporting the entire surface roughness parameters (Sa, Sq, and Sz)

[293] provides a greater understanding of the roughness over the entire surface measured as compared to just the line measurement which could vary based on line location. From

Figure 27, it was determined that the average surface roughness (Sa), root mean square roughness (Sq) and mean roughness depth (Sz) had values of 0.18 microns, 0.24 microns, and 4.95 microns, respectively. On the other hand, Figure 28 showed that the phosphorene

membranes showed higher values of Sa = 0.45 microns, Sq = 0.61 microns, and Sz = 6.46

microns. With phosphorene nanoparticles synthesized using the basic exfoliation technique

agglomerates in water, agglomeration might be a cause of the observed increase in roughness of the phosphorene membranes since while phosphorene was added to the dope containing NMP, the non-solvent of the phase-inversion membrane casting process was water.

(A) (B)

Figure 27: (A) three dimensional and (B) bottom view of SPEEK: PSf membranes showing the surface morphology

(A) (B)

Figure 28: (A) three dimensional and (B) bottom view of phosphorene membranes showing the surface morphology

Previous studies also provided other morphologically parameters associated with the polymer evolution due to the addition of phosphorene [216]. The pore diameter at the

100

maximum pore distribution that is, the most prevalent pore size of the SPEEK:PSf

membranes was on average 0.022 microns (with smallest and largest detected pores being

0.017 and 0.086 microns), while that of the phosphorene membranes averaged 0.0024

microns (with smallest and largest detected pores being 0.0022 and 0.0078 microns). This

further indicates the addition of phosphorene accumulating within the pores in agreement

with agglomeration results. Furthermore, the contact angles of SPEEK:PSf and phosphorene membranes were found to be 48.3° ± 0.67 and 81.5° ± 0.64, respectively, and

the increase in hydrophobicity was associated with the presence of the more hydrophobic

phosphorene [237]. Lastly, it was observed that at a pH of approximately 6, the zeta potential of SPEEK:PSf was -61 ± 4.6 mV while that of the phosphorene membranes was

-44 ± 7 mV, which was due to the phosphorene nanoparticles masking some of the sulfonic

sites.

5.3.5. Phosphorene Leaching

The transport of two-dimensional phosphorene in porous media is largely dependent on the

pH [294]. At a pH far away from the pH of the point of zero charge (pHZPC), also known

as the isoelectric point, the repulsive forces on the electric double layer on hydrated nanoparticles decrease, as a result there is lower aggregation and more dispersity [295].

The pHZPC of hydrated phosphorene is 3.0 [250]. Phosphorene nanoparticles were

incorporated into membranes and their stability under acidic, basic, and neutral

environments were determined using the ICP-OES. As seen in Figure 29, generally the nanoparticles seemed to be stable under all three conditions, with less than a 1% loss in amount of phosphorene. Under the basic medium though, irrespective of the initial

101

concentration of phosphorene, the loss of phosphorene was highest, as compared to other media. This could be as result of the pH of the basic media being too far from 3.0 thus leading to the lesser aggregation and more detectable free phosphorene. This factor also explains why as the concentration of phosphorene increased the basic dissolution increased.

Figure 29: Leaching experiment of phosphorene in membrane 5.3.6. Pore Structure Comparison

Pore size and porosity largely determine the efficiency of separation [296], and these properties of the membrane are controlled by the fabrication technique [232]. These techniques include phase separation processes [297], stretching, track etching [298] and sintering [299] amongst others. For phase separation processes that use immersion precipitation like the nonsolvent-induced phase separation (NIPS) technique, liquid-liquid demixing controls the morphology of the membrane [296]. The structure of membranes obtained via phase immersion precipitation can be classified under five broad categories based on the polymer, solvent, and non-solvent combination. They include noodles,

102

cellular structures, macrovoids, bicontinuous structures and unconnected latex [300].

Membranes formed via the NIPS technique involving a solvent/nonsolvent combination of

NMP and water, macrovoids (fingerlike in large quantities and pear shaped like in small quantities) are typically the kind of structures that represent a large portion of the membrane morphology [296, 301]. Nodules, spherical beads which are fused together, are also typically observed on the surface layer, the layer where most separation occurs [302].

From the SEM images of both phosphorene and SPEEK: PSf membranes Figure 30, nodules were observed on the surface scans and they gradually turned into macrovoids as expected based on the solvent/non-solvent combination used during the preparation of the membrane. Both membranes exhibited similar morphological structures at the top and middle layers, but towards the bottom layer, there were noticeable differences, the SPEEK:

PSf membranes merged into spherical macrovoids, while the phosphorene membranes retained its nodular/finger-like structures. This is similar to published studies using silver nanoparticles; thus, nanoparticles can act as pore formers increasing the length of the finger-like structures[280, 281]. This was controlled by the low addition of phosphorene to the membranes, which again is based on observations from previous studies that used other nanoparticles.

103

40µm 40µm

(A) (B) Figure 30: Cross-section images of (A) SPEEK: PSf membrane, and (B) and phosphorene membrane

5.3.7. Phosphorene Distribution on the Membrane

To ascertain the location of phosphorene nanoparticles within the membrane, a depth profile scan was performed on the membrane. As seen in Figure 31, phosphorus was found to be present on the surface of the membrane and the amount increased as the etch time increased, thus indicating that phosphorene was also present within the pores of the membranes. That is, even though there was some agglomeration of membranes, which was attributed to the increase in roughness observed, phosphorene was still found to be dispersed throughout the membrane matrix.

104

Figure 31: Depth profile scan on phosphorene membranes

5.3.8. Flux Discussion

The phosphorene membranes showed a rejection of 78 ± 4% for BSA, while rejection for the SPEEK: PSf membranes was 43 ± 16%. This can be explained by the pore size of the membranes. Bovine serum albumin has a molecular weight of 66 kDa. The mean pore

diameter of SPEEK:PSf and phosphorene membranes had been previously determined to

be 0.022 microns and 0.0024 microns [216], respectively. With respect to permeability,

Figure 32 (A) shows that for SPEEK: PSf membranes, the average initial flux was 100 ±

105

12LMH, final flux 23 ± 3 LMH and recovered flux after reverse flow filtration 65 ± 9

LMH. For phosphorene membranes (Figure 32 B), the initial flux was 86 ± 40 LMH, final

flux 8 ± 6 LMH and recovered flux after reverse flow filtration 30 ± 14 LMH. The smaller

pores of the phosphorene membranes along with increased hydrophobicity might have led

to observed rejection values along with reduced the flux values observed with phosphorene

membranes. The low observed recovered flux after reverse-flow filtration also indicates an increase in the organic matter fouling layer on the phosphorene membrane, which agrees with the increased hydrophobicity of the membranes and decreased surface charge.

(A) (B)

Figure 32: (A) Flux analysis of SPEEK: PSf membranes and (B) Phosphorene membranes

106

5.3.9. Operational Performance of Phosphorene Membranes

BSA filtration results show that while the rejection was increased, the flux during operation decreased, and more concerning, a fouling layer accumulated. BSA has an isoelectric point at pH 4.5–5.0 [303], so the protein is negatively charged at the neutral pH values of operation. BSA is also a large molecule of approximately 66.5 kDa. To study both the irreversibility of fouling and the potential of an ultraviolet (UV) light response by phosphorene membranes, the filtration of methylene blue (MB) was used so that the fouling layer could be visually observed. MB was chosen since it is known to degrade under UV light, is a hydrophobic and basic dye (MB+), and has an approximate 300 Daltons; therefore, while smaller than BSA, it was expected to more irreversibly adsorb to membranes as compared to BSA. Studies were performed using both visible and UV light sources to determine if an improvement was observed. Table 3 summarizes the flux values obtained, all performed at a constant pressure of 2.06 bar.

Table 3: Flux values of phosphorene membranes operated under visible and UV light sources SPEEK: PSf Membranes Phosphorene Membranes

Flux (LMH) Visible UV Visible UV

PWF Initial 126 67 56 107

PWF Final 92 37 74 82

MB Initial 72 42 71 68.1

MB Final 43 29 42 31

Recovered 40 17 25 70

Normalized Membrane Surface Coverage (%) 100 95 76 30

107

SPEEK: PSf membranes operated both under visible and UV light sources showed large declines in flux during MB filtration. Furthermore, cleaning using reverse flow filtration did not show any recovery in flux; therefore, membranes were irreversibly fouled. On the other hand, for phosphorene membranes, under visible light, the recovered flux after reverse-flow filtration to simulate cleaning with pure water was low, indicating an irreversible accumulation of MB on the membrane surface. This agrees with BSA filtration results that showed a decline in flux during BSA filtration along with a small flux recovery.

However, when phosphorene membranes operated under a UV light source, a full recovery of flux after reverse flow filtration was observed. Membrane surfaces were then imaged and surface coverage, shown in Table 3, supports the removal of MB from the membrane surface. However, it was beyond the scope of this study to determine if the removal of the

MB layer was physical (due to desorption) or chemical (due to degradation).

5.3.10. Toxicity of Phosphorene

The effect of a phosphorene exposure was tested on C. elegans mortality and reproduction in two different media, which differed by ionic strength and pH. The exposure in K- medium with higher ionic strength and lower pH of 5.8 demonstrated lower toxicity than exposure in MHRW with higher pH of 7.8 and lower ionic strength. In fact, there was no mortality observed when the nematodes were exposed in K-medium with Phosphorous concentration up to 60 mg/L. From Figure 33, the exposure in MHRW resulted in concentration-dependent mortality with increase observed only at Phosphorous concentration of 45 mg/L and above.

108

For reproduction, a low toxicity was documented in both media (Figure 34). Reproduction

is more sensitive endpoint than mortality, and there were decreases in C. elegans

reproduction at Phosphorous concentrations at 12 mg/L in K-Medium and at 2.2 mg/L in

MHRW.

These results demonstrate that toxicity of phosphorene in free form depends on the

exposure media and it is critical to ensure that no leaching of phosphorene occurs when

these nanoparticles are incorporated into a membrane. We have measured concentration of

phosphorous in the permeates of the first, third and fifth order of filtration performed

through the phosphorene membrane with K-Medium or MHRW. The levels of the phosphorous in the permeates were all below detection limit and there was no toxicity observed when the nematodes were exposed to the permeates. Thus, our results demonstrate that even though there was a reproductive toxicity observed in C. elegans

exposed to free phosphorene, the release of the phosphorene from the membrane was

minimal or none and will not caused toxicity. This is a step in the right direction of

developing safe polymeric phosphorene membranes that can be eventually applied in

removal of organic pollutants. Since the relatively low toxicity was observed for the

phosphorene exposures, it is imperative to examine effect of phosphorene on toxicity under

different conditions as well as effects of phosphorene on other sub-lethal endpoints. For

instance, our results above showed that less than 1% release of phosphorene from the

membranes can occur at basic conditions, and thus further studies are warranted to examine

additional factors that might promote phosphorene release.

109

Figure 33: Caenorhabditis elegans mortality in response to phosphorene exposure over 24 h in Moderately Hard Reconstituted water (MHRW). The double asterisks indicates statistical significance at p < 0.01.

Figure 34: Effect of free phosphorene exposure over 24 h on reproduction in Caenorhabditis elegans in A) K-Medium and B) Moderately Hard Reconstituted Water (MHRW). The double asterisks indicates statistical significance at p < 0.01.

5.4 Conclusions

Phosphorene membranes were synthesized to further characterize the evolution of the

polymeric membrane fabrication upon addition to phosphorene. It was observed that

phosphorene formed spherical distinct nanoparticles after exfoliation in basic-NMP and

110

clustered spherical nanoparticles in water because of the effect of the flux of hydrogen ions

(H+) within the nanoparticle system. In leaching studies, it was observed that phosphorene loss was less than 1% of the initial amount of phosphorene added, implying stability within the membrane matrix. Depth profile scans of phosphorene membranes showed that phosphorene nanoparticles were dispersed both on the surface of the membrane and within the pores of the membrane, indicating that while agglomeration might have occurred, phosphorene was still dispersed throughout the membrane matrix. Surface morphology studies indicated that phosphorene membranes had rougher surfaces, while the SPEEK:

PSf membranes had smoother surfaces, which was likely due to some agglomeration caused by water being used as the nonsolvent during membrane fabrication via NIPS. The membranes modified with phosphorene displayed a higher protein rejection but lower flux values and flux recovery after filtration possibly due to the decrease in average pore size.

Toxicity results show that exposure to a phosphorene in a free form caused a relatively low toxicity in C. elegans with reproduction being a more sensitive endpoint than mortality. In addition, toxicity differed when exposures were conducted in two different media with

MHRW showing higher toxicity. However, permeates of the same media through phosphorene membrane did not show toxicity due to minimal release of the phosphorene from the membranes further buttressing that phosphorene remained bound during filtration.

Thus, phosphorene-based membranes open a new field for research in membrane science since phosphorene nanoparticles synthesized were found to be stable within the membrane structure, with less than 1% leaching of phosphorene. The toxicity of the free phosphorene indicate that it is critical to continue studies examining fate of phosphorene incorporated

111

into the membranes under different environmental conditions to develop safe phosphorene membranes.

112

CHAPTER 6. Dual Functional Phosphorene Nanocomposite Membranes for the Treatment of Perfluorinated Water

This chapter will be submitted to a journal for publication Joyner Eke1, Lillian Banks1, Abdul Mottaleb2, Andrew Morris2, Olga V. Tsyusko3 and Isabel C. Escobar1,* 1 Center of Membrane Sciences, Department of Chemical and Materials Engineering, University of Kentucky, 177 FPAT, Lexington, KY, USA, 40503 2 College of Medicine, University of Kentucky, Lexington, KY, 40506-0046, USA 3 Department of Plant and Soil Sciences, University of Kentucky, 1100 S. Limestone St., Lexington, KY, USA, 40506 * Correspondence: [email protected]

6.1. Introduction

Based upon the success of graphene, two dimensional (2D) materials have excited

scientists worldwide. As a result, much research has been tailored towards developing the

next generation of materials that may be able to overcome one of the main limitations of

graphene, which is the absence of a band gap [304]. Phosphorus which constitutes

approximately 0.1% of the Earth’s crust is one of the most abundant elements [11], and it

exists as several allotropes. White and red phosphorus are the most commonly seen

allotropes used typically for making explosives and safety matches [12]. Black phosphorus

(BP), though rarely mentioned, is the most stable allotrope of phosphorus [13], and it

combines high carrier mobility with a fundamental band gap [14]. Graphite and black

phosphorus (BP) are the only known monotypic van der Waals crystals [15, 16]. Unlike

carbon, phosphorus has only three valance electrons which leads to BP being

semiconducting since each atom is bonded to three neighboring atoms [15]. Exfoliated, p- 113

type semiconducting BP flakes possess mobilities of ~200-1000 cm2 /V-s at room

temperature, current on/off ratios of ~104 and anisotropic transport. Consequently, BP

shows promise as a nanomaterial that could complement or exceed the electronic,

spintronic, and optoelectronic properties of graphene [17, 18]. Phosphorene is the single

atomic layer of BP that shows semiconducting properties [19]. Phosphorene distinguishes

itself from other 2D layered materials by its unique structural characteristics, relatively

large direct bandgap and good charge carrier mobilities [20]. These semiconducting

properties of phosphorene have the potential to be explored in making low fouling surfaces,

such as for membranes, and for contaminant removal. Recently, phosphorene has been

used as an additive to produce stable nanohybrid membranes highly selective for molecules

and ions [305].

Perfluoroalkyl substances (PFAS) are a group of man-made surfactant chemicals that were

first produced in the 1940s. PFAS can be found in many consumer products including food

packaging, household cleaners and fire-fighting foams. PFAS are a concern because they

do not degrade, are very persistent in the environment, and have been found in the

environment in remote locations [306]. PFAS are organic fluorochemicals where at least one carbon-hydrogen bond on the hydrocarbon chain is replaced by a fluorine-carbon bond.

Fluorine is one the most reactive elements when not bonded, but when it has been bonded, it is extremely stable. Fluorinated hydrocarbons are resistant to high temperatures, strong acids and bases, and are nonflammable as well [307]. This stability of PFAS makes it virtually nondegradable and allows for PFAS to build up in the environment, in marine animals and mammals, including humans. There have been several studies performed that show evidence of PFAS having adverse effects on human health because of their

114

environmental persistence and widespread human exposure and toxicity [308-310]. They

are extremely persistent in the environment because they possess both hydrophobic

fluorine-saturated carbon chains and hydrophilic functional groups, along with being

oleophobic [311]. PFAS have been shown to have carcinogenic properties as well as

developmental toxicity [307, 312]. As the chain length of the compounds increases so does

the toxicity of their effects [313]. In 2009, the EPA labeled two PFAS substances,

perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonate (PFOS), as contaminants of potential concern in drinking water[314], and it has set a lifetime health advisory at 70 ng/L for PFAS in drinking water [315].

PFOA and PFOS are two of the most common PFAS substances produced and have now been banned from being produced in most of Europe and the United States. The degradation of PFOA, leads to the formation of two intermediate products, which are less fluorinated carboxylic acids and shorter-chain PFASs. The presence of the carboxylic acids indicates the cleavage of C−F bonds and H/F exchange, while formation of short chain

PFASs implicates the scission of C−C bonds [316]. The treatment technologies currently available for the removal and/or degradation of PFAS compounds are limited to adsorption,

advanced photochemical oxidation, sonochemical decomposition, filtration, and air- sparged hydrocyclone technology [166]. For adsorption, granular activated carbon in the absence of organic matter is effective for the removal of long chain perfluoroalkyl acid,

but it is ineffective against short chain perfluoroalkyl acids[167]. Sonolysis involves the

use of ultrasound waves to create cavitation. During the process of cavitation, bubbles

collapse and adiabatically generate high pressure and temperature conditions that pyrolyze perfluorinated compounds [169]. Sonolysis has been observed to breakdown PFAS

115

compounds on the laboratory scale, but it has not been commercialized because of design

challenges during the cavitation propagation [167]. Advanced oxidation processes that have successfully degraded PFAS include ultraviolet (UV) irradiation and electrochemical techniques[170]. Photochemical oxidation is an indirect photolysis technique which

degrades contaminants by reacting with reactive radicals. Adding a photocatalyst to UV

photolysis of PFAS enhanced the ability of the process to degrade the material [171].

2 3 2− 4- 2− Catalysts such as TiO , Fe +, S2O8 , IO , and CO3 , in combination with UV efficiently

degraded PFAS owing to formation of reactive and potent oxidative species such as CO3-

• , H• , OH• , and PFAS complexes[172]. Direct photolysis of PFASs tends to have

relatively low removal efficiencies and fluoride yields compared with other processes and

thus needs additional processes to reach complete degradation [171].

Oxygen is a cheap, abundant and green oxidant, which usually generates water as the only

stoichiometric byproduct, and recent research efforts have been tailored towards the

development of liquid phase aerobic oxidation methods to combat the negative impact of

the inorganic oxidants, like potassium permanganate, chromium trioxide, and manganese

dioxide[317]. Under ambient conditions, oxygen in its ground state is unreactive with

organic molecules; hence, a catalyst is often necessary to control the selective oxidation of

a molecule[318]. Palladium catalyzed aerobic oxidations are the most studied and have

been successful in the conversion of alcohols to ketones and aldehydes [319].

Recently, a temperature-responsive membrane composed of poly-N-isopropylacrylamide

(PNIPAAm) on polyvinylidene difluoride (PVDF) membranes acted as polymeric

adsorbent to remove PFOA successfully [320]; however, PFOA was not destroyed.

116

Therefore, there is a critical need for safe and efficient remediation methods for PFAS, particularly in drinking water.

Nanocomposite membranes with tunable properties show promise for numerous technologies [1-4] because of their size-dependent electronic structure and controllable physical properties. The purpose of this research is to develop and validate environmentally safe nanomaterial-based approaches for treatment of drinking water including degradation of per- and polyfluorinated chemicals (PFAS). Specifically relevant to the field of liquid separations using membranes, the band gap of phosphorene provides electronic [221] and photocatalytic [179] properties, which are proposed to make reactive membranes to simultaneously remove and destroy PFAS. With the high toxicity and corrosive issues encountered with metal-based photocatalysts (oxides, sulfides and nitrides of titanium, tungsten, cadmium and transition-metal dichalcogenides), phosphorene can act as a metal- free photocatalyst to degrade organic compounds in the feed solution to make reactive membranes. In this study, charged nanofiltration membranes were synthesized by blending polysulfone (PSf) with sulfonated poly(ether ether ketone) with phosphorene nanoparticles. The goal of this study was to assess the potential of phosphorene membranes for contaminant removal. Here, a nanohybrid nanofiltration (NF) membrane with tailored selectivity for the removal of PFOA was used. After filtration, the removal and/or destruction of the PFOA that accumulated on the surface of the membranes was investigated using UV and oxygenation as treatments. Figure 35 shows a schematic of the experimental process.

117

Figure 35: Schematics of the experimental process

6.2. Materials and Methods

6.2.1. Materials

Perfluorooctanoic acid (PFOA) was purchased from Sigma Aldrich (St Louis, MO, USA).

For the sulfonation reaction, polysulfone (PSf), N-methyl pyrrolidone (NMP), poly ether ether ketone (PEEK), and concentrated sulfuric acid were purchased from VWR (Radnor,

PA, USA). Black phosphorus used for the synthesis of phosphorene was purchased from

Smart Elements (Vienna, Austria) and the ultrasonicator model P70H was purchased from

Elmasonic P, Singen, Germany. For membrane filtration studies, the dead-end cell,

Amicon Stirred Cell 8010–50 mL, was purchased from EMD Millipore (Burlington, MA,

USA).

118

6.2.2. Preparation of phosphorene

Phosphorene was synthesized by chemically exfoliating black phosphorus according to previously described techniques [22, 216]. In summary, NMP and NaOH with a volume

ratio of 1:1 were mixed and degassed on an ultrasonicator (P70H, Elma Elmasonic P,

Singen, Germany) for five minutes. Then, 100 mg of black phosphorus was introduced into the mixture and sonicated for five hours at frequency and power of 37 KHz and 80%, respectively. The temperature of 30 ˚C was maintained throughout the experiment. This was then followed by centrifugation at 4000 rpm for 23 minutes. After centrifugation, the supernatant was collected and used for the experiment.

6.2.3. Sulfonation of poly ether ether ketone

Poly ether ether ketone was sulfonated as previously described [216]. Briefly, PEEK pellets were oven dried at 60˚ C overnight, after drying the pellets were dissolved in concentrated sulfuric acid solution (98%) for three days until a homogenous solution was formed at 25 ˚ C. The solution was gradually added into an ice water bath which was vigorously stirred to precipitate SPEEK (sulfonated poly ether ether ketone) polymer.

SPEEK was washed in deionized water until a pH of 7 was achieved. Then it was oven dried at 60˚ C and stored for usage.

6.2.4. Water Flux Analysis

The membrane used in this study was a polymeric blend of polysulfone and SPEEK, the process has been described here[238]. The dope solution was a (95/5%) ratio of PSf and

SPEEK, and 0.5 volume wt.% of exfoliated phosphorene in NMP. Dead-end filtration studies were performed using a 50-mL Amicon stirred cell (Millipore Sigma, Burlington, 119

MA, USA) under continuous stirring in a batch mode. A Whatman filter paper (110 mm) was used as a support for the membranes during the experiment. The filtration was done under a constant pressure of 2.06 bar at room temperature. The time for 2 mL of water to pass through membranes with an area of 13.4 cm2 was recorded, and the water flux, J

(LMH), was calculated using equation 1

J = 𝑉𝑉 (1) 𝐴𝐴𝐴𝐴𝐴𝐴 where V is the volume of solution through the membrane in L, and A is the active filtration area of the membrane cell in m2, and t is the permeation time.

6.2.5. Determination of the water interaction parameter of the membranes

A drop shape analyzer (Kruss DSA100, Matthews, NC, USA) was used to determine the wettability or water interaction parameter of the membrane by estimating the contact angle between water and the solid surface of the membrane. The wettability of a membrane surface plays a key role in water permeability and fouling[321]. For a liquid drop on a flat horizontal surface, the contact angle can be described as the tangential angle formed at the point of contact of the liquid on the solid surface. It denotes the equilibrium point of all surface tension forces acting on the boundary layer at the point of contact[321]. A contact angle value lower than 90° typically implies hydrophilicity of the material and values greater than 90° usually denotes hydrophobicity.

6.2.6. Treatment Processes

After filtration of PFOA through the membrane, the membranes were removed and treated using two methods, as shown in Figure 35. The first was a photolysis system consisting of

120

UV irradiation of the catalytic phosphorene membrane, while the second was a liquid

aerobic oxidation system consisting of oxygenating the catalytic phosphorene membrane.

For the first setup, ultraviolet irradiation was supplied with a UV lamp (Spectroline Model

EA-160, Westbury, NY, USA) at 365 nm. The membranes were exposed for 200 minutes

and experiments were performed in the dark. For the second setup, oxygen was bubbled at

a constant flowrate of 3L/min onto the surface of the membrane for 280 minutes,

experiments were performed under visible light. These time durations were chosen based

on previous trial experiments. A series of tests were conducted and after 120 minutes, removal of PFOA had not happened, hence we decided to increase experimental time. This can be found in the supplementary materials. After treatment, the membranes were cleaned by reverse flow filtration and the permeates from the backwash process were tested for

PFOA. Equation 2 was used to determine the rejection of PFOA in the permeates.

R = (1 − (Cpr/Cs)) × 100% (2)

Where Cpr is the PFOA concentration in the permeate after reverse flow filtration and Cs

is the concentration on the membrane surface which is calculated from the difference

between initial PFOA feed concentration Cf and concentration of PFOA in the permeate after filtration CP

6.2.7. Membrane fouling analysis

To study the fouling control performance of the membranes, PFOA at a concentration of

100 mg/L was filtered. The fouled membranes after filtration were subjected to two

treatment methods: photolysis by irradiation with ultraviolet light (Spectroline Model EA-

160, Westbury, NY, USA) at a wavelength of 365 nm and catalytic oxygenation by

121

bubbling oxygen on the surface of the membranes in water after filtration. This was

followed by reverse-flow filtration of deionized water to eliminate dissolved foulants from

the treatment steps and determine flux recovery of the membrane. The flux of the PFOA

solution Jp (LMH) and the flux of the cleaned membrane, Jr were measured at 2.06 bar. The flux recovery (FR) was estimated using equation 2 [322]. The higher the flux recovery, and the lower the total fouling ratio, the higher the antifouling property of the membrane[323].

FR(%) = ( ) × 100 𝐽𝐽𝐽𝐽 𝐽𝐽 (2) The fouling resistance of the membrane was evaluated using equations 3,4 and 5[322] ,

where Rt , Rr , and Rir represent the total fouling ratio (which indicates the total flux loss

from fouling), reversible fouling and irreversible fouling respectively.

Rt = ( 1 ) × 100 𝐽𝐽𝐽𝐽 𝐽𝐽 (3)

Rr = ( ) × 100 𝐽𝐽𝐽𝐽−𝐽𝐽𝐽𝐽 𝐽𝐽 (4)

Rir = ( ) × 100 𝐽𝐽−𝐽𝐽𝐽𝐽 𝐽𝐽 (5) The PFOA rejection of the membrane after filtration and after during reverse flow filtration

after each treatment method was determined using equation 6

R = (1 − (Cp/Cf)) × 100% (6)

Where Cp is the PFOA concentration in the permeate and Cf is the concentration in the

feed. The concentration of PFOA was determined using an liquid chromatography-tandem

mass spectrometry (LC-MS/MS) method for per-/polyfluoroalkyl substances from water,

122

according to the one used by Saad et al. [320]. Essentially, we employed our previously

developed and reported the LC-MS/MS method for per-/polyfluoroalkyl substance (PFAS) analysis [324, 325]. Briefly, PFOA was measured by ultra-performance liquid chromatography (UPLC ) coupled electrospray ionization tandem mass spectrometry. A bench top binary Shimadzu chromatograph (Model: LC-20 AD) and SIL 20 AC autosampler interfaced with an AB SCIEX mass spectrometer (MS/MS) (Model: 4000 Q

TRAP) were used. In this study, since PFOA was target analyte, mass labeled perfluoro-

13 n-[1,2,3,4- C4] octanoic acid as surrogate standard (SS), and mass labeled perfluoro-n-

13 [1,2,3,4- C4] heptanoic acid as internal standard (IS) were used. Filtered and diluted water

samples (1.0 mL) were prepared containing 40 ng/L SS and 20 ng/L IS. The SS spiked

samples, continuous calibration verification (CCV), reagent blank and IS-blank were used

as quality controls (QC). Target analyte concentrations and QC performance of the method

were determined using IS based calibration curves. A gradient elution of mobile phase

containing 20 mM ammonium acetate in pure water (A) and pure methanol (B) was used

with a Macherey Nagel analytical column EC 125/2 NUCLEODUR C18 gravity packed

with 5 µm particle (length 125 x 2 mm ID) at a constant flow rate of 0.4 mL/min. A 13.51

min gradient with composition of B was started 40% at 0.01 min, 65% at 1 min, 90% at 6

min, 95% at 11.5 min, 40% at 13.51 min with 2 min equilibration time. A volume of 5 µL

of standard or samples was injected. Data were collected in negative multiple reaction

monitoring (MRM) mode with monitoring of quantitation and qualifier ions for PFOA, SS

and IS. Data acquisition and process were performed using AB Sciex Analyst version 1.4.2

and Multiquant version 3.0 software, respectively. The precursor and product ions

monitored were PFOA 412.912 > 368.7, 168.7 m/z; SS 416.946 > 371.9 171.7 m/z; IS

123

366.897 > 321.7, 171.6 m/z were obtained. Bold face indicates the quantitation ions. The

PFOA, SS and IS were eluted from column at retention times of 6.57, 6.58, 6.03 min,

respectively. Average spiked SS recovery was 99.2% and average analyte CCV recoveries

105.4%. Limit of detections (LOD) for target analytes were 0.25 ng/mL at S/N= 4. Seven

calibration points with linear dynamic range (LDR) were 1.0 - 160 ng/mL with R2 values

of 0.9986. MS was operated with curtain gas 30 psi, negative ESI 4500-volt, temperature

300 oC, and ion sources gas (GS1/GS2) 30 psi.

6.2.8. Structural and profile studies with Scanning Electron Microscope (SEM) and X- ray photoelectron spectroscopy (XPS)

SEM studies were carried out to examine the surface characteristics of the membrane after fouling with PFOA. The membranes were first submerged and broken in liquid nitrogen to achieve a fractured surface with negligible deformation (stretching and tearing) of the polymeric membranes. Surface images were obtained with the resulting fracture in a scanning electron microscope (SEM), Quanta FEG 250, FEI (ThermoFisher Scientific,

Waltham, MA, USA) without conductive coating.

The atomic profile compositions of the membranes were determined using a using a Thermo Scientific (Waltham, MA, USA) K-Alpha XPS apparatus equipped with an Al

K (1486.6 eV) source (pass energy of 20 eV). Scans were conducted on the surface and a

depth profile study was done on different regions to quantify the presence of fluorine and

carbon in the membranes after each treatment method. XPS characterization of

phosphorene membranes was performed. Phosphorus, carbon, oxygen, and sulfur, fluorine

peaks were fitted using Thermo Scientific™ Avantage Software. The emission current of

124

the X-ray source was 12 mA while the acceleration voltage was 10 kV. The spectra

measurement was performed at an emission angle of 90o. The electron energy analyzer

operated in FAT mode (Fixed Analyzer Transmission), with a pass energy of for survey

scans and high-resolution scans of 50 eV and 20 eV, respectively. The total resolution of

this XPS was about 1.1 eV.

6.2.9. Surface roughness characterization

For nanofiltration membranes, factors that affect the extent of fouling irrespective of

foulants on the membrane include membrane surface roughness, surface charge, and

surface hydrophobicity[211]. The surface roughness of the membranes was measured after reverse flow filtration to determine the effect of PFOA fouling on the roughness of the membrane using an atomic force microscope (AFM) (Bruker Dimension Icon, Santa

Barbara, CA, USA). A membrane area of 20 × 20 µm was chosen. Data was collected under tapping mode and evaluated by the average root-mean-squared (RMS) roughness.

6.3. Results and Discussion

6.3.1. PFOA Filtration Studies

To study the permselectivity of the membranes towards PFOA, filtration studies were performed by filtering a 100 mg/L PFOA solution through the phosphorene membranes using crossflow filtration. The filtration flux profile is shown in Figure 36A, with all filtration experiments being performed at a pressure of 2.06 bar. From Figure 36A, during membrane precompaction, the initial and final pure water flux values of the membrane were 195 ± 14 LMH and 150 ± 31 LMH, respectively. At the end of precompaction, defined 125

as once the pure water flux becomes constant, the PFOA filtration was started. The initial

and final flux values for PFOA filtration were 145 ± 40 LMH and 123 ± 29 LMH. The flux

after reverse flow filtration, used to simulate backwashing to remove reversible attached

foulants, was 163 ± 9 LMH; hence, the flux recovery was 84%. On average, total fouling

ratio of the membranes was 26%, the reversible resistance of the membrane was 10% and

the irreversible resistance of the membrane was 16%. This indicates that the membranes

were moderately irreversibly fouled. The high flux recovery along with the low total

fouling ratio indicate a high anti-fouling property [323]; therefore, the phosphorene

membranes were able to successfully control PFOA fouling. The standard deviations

observed come from the variabilities that arise during the casting process. For example, the

thickness of a membrane is partially responsible for the value of the flux through the

membrane, with thicker membranes displaying lower flux values as compared to thinner

membranes. While a doctor’s blade tool allows for setting of the desired thickness, spatial

variations in laboratory-cast membranes are still common and possible [326]; hence, the

high standard deviations. Flux declines were normalized to the initial flux for each duplicate filtration experiment (Figure 36B), and upon averaging those, the standard deviations decreased supporting the notion that spatial variations associated with casting were responsible for the larger differences between runs.

Furthermore, PFOA was almost completely rejected by the membrane with a rejection of

99.9%. This excellent selectivity for PFOA with these membranes can be ascribed to two factors, size exclusion, based on pore size, and electrostatic repulsion between the membrane and the acid. The molecular weight of PFOA is 499 Da [327] or <0.14 μm [328], while previous studies have shown the average pore size of the phosphorene membranes

126

was 0.0024 microns [216], so they were able to easily reject PFOA based on size exclusion.

Furthermore, under neutral pH values, PFOA exists as the fully ionized component

(COO−), so negatively charged [329], while under the same conditions, the membranes

have also been previously shown to be negatively charged [216]. Therefore, the complete

rejection of PFOA was further aided by electrostatic repulsion [330].

A B

Figure 36: (A) Flux results (liters/m2-hr) for the phosphorene membrane at a constant pressure of 2.06 bar, showing the initial precompaction period, where pure water was filtered through the membranes until a near-constant flux value was attained. After precompaction, the filtration of PFOA was carried out, and it was followed by reverse flow filtration to simulate backwashing. (B) Normalized flux decline.

127

6.3.2. Hydrophobicity

Perfluoroalkyl chains can exhibit hydrophobic and hydrophilic tendencies because of the presence of fluorinated compounds, which introduce hydrophobicity, and of carboxylic groups that introduce hydrophilicity [331]. The rigidly bound, non-bonding electron pairs

that surrounds each fluorine atom in the C-F bonds present in perfluoroalkyl compounds are not easily polarized and thus prevent hydrogen bonding with polar and non-polar compounds. This increases with the degree of fluorine substitution at each carbon center and relies on the length of the perfluoroalkyl chain. Thus, longer perfluoroalkyl chains exhibit oleophobic properties, while shorter chains exhibit hydrophobic tendencies [332].

From Figure 37, the measured contact angle of the membrane before filtration was 70.39

± 0.13◦. After PFOA filtration, the contact angle did not change, and it was 70.87± 0.39◦.

After irradiation with ultraviolet light, the membranes became more hydrophilic with a contact angle of 62.7± 0.04◦. This may be due to the formation of hydrophilic formic acid after the photolysis reaction. Formic acid is one of major byproducts of PFOA photolysis by UV irradiation [333]. On the other hand, the membranes became more hydrophobic after catalytic oxygenation with a contact angle of 82.3±0.15˚, which may be due to the breakdown of PFOA into smaller perfluorinated groups since these groups have stronger

C-F bonds and are very hydrophobic.

128

No filtration No treatment UV Oxygenation

100

40 Contactangle

0 0 1 2 3 4 5

Membrane treatment Figure 37: Water interaction parameter graph, to represent different levels of hydrophobicity, for the different membrane surface treatment techniques studied.

6.3.3. Fouled PFOA Removal

After PFOA was filtered through the membrane, the membranes were subjected to two

treatment techniques to breakdown the PFOA adsorbed or fouled onto the membranes.

Upon analysis of the permeates after each treatment for adsorbed PFOA, the PFOA

removal is presented on Figure 38 as a function of the type of treatment used. Membranes that were subjected to UV irradiation for 120 minutes had a removal of 91.95. ± 1.6% of the PFOA that reversibly fouled the membranes. Membranes subjected to UV irradiation for 200 minutes had a removal of 98.4 ± 2.42%. Membranes subjected to oxygenation for

120 minutes displayed a removal of 91.8 ± 0.02%, while oxygenation for 200 minutes 129

increased removal to 96.55± 4.1%. Lastly, oxygenation for 280 minutes showed a minor

decrease in removal to 94.8 ± 4.59%. This suggests that both treatments, UV irradiation

and oxygenation, were effective in removing the PFOA reversibly bound to the

membranes. An underlying reason would be the photocatalytic properties of the membrane

itself. Phosphorene-modified membranes have previously been observed to display

tendencies for photocatalysis of organic compounds [216]; thus, it is proposed here that the

PFOA was broken down into smaller compounds during treatment. These further buttresses the atomic profile scan results of the membrane surface and pores, where little to no fluorine molecules was detected in all the membranes. UV irradiation for 200 minutes had the highest adsorbed PFOA removal value because of phosphorene’s stronger light

interaction with UV at 365nm[216]. Furthermore, there was no fluoride detected, as

measured by IC, in the reverse flow filtration samples from the membranes with no

treatment or after they were exposed to UV and oxygenation. This suggests that, while

PFOA is likely to break down into smaller chain compounds under treatments.

130

Figure 38: Removal of PFOA from the surface of the membrane after UV irradiation for two different periods of time, and after bubbling of oxygen for three different periods of time.

6.3.4. Membrane Morphology

To further understand and visualize the effects of each treatment on the fouled membrane,

SEM surface images were taken after reverse flow filtration. Figure 39A shows the surface images of the clean membrane, the membrane after filtration of PFOA (Figure 39B), the membrane after filtration of PFOA and irradiation with UV (Figure 39C), the membrane after filtration of PFOA and oxygenation (Figure 39D). Organic fouling is often characterized by the presence of a thick layer on the membrane surface[334]. Advanced oxidative processes can breakdown organic compounds by either altering their functional groups or dividing major aromatic moieties into smaller compounds, such as aliphatic

131

organic acids [335]. From Figure 39, it was determined that membranes that were exposed to UV irradiation were the least fouled, followed by the filtration alone membranes, and lastly membranes that were oxygenated. However, despite seeming to have the largest amount of fouling of their surfaces, the fouling on oxygenated membranes looked smaller in size and looser as compared all the other membranes. The presence of smaller compounds on the oxygenated membrane might be due to the generation of hydroxyl radicals during the treatment because studies have shown that PFOA oxidation by hydroxyl radicals happens following a stepwise mechanism where the cleavage of the carbon-carbon bond and the carboxylate group results in the generation of shorter chain perfluorinated groups [336], which also agrees with the observed increase in hydrophobicity (or contact angle) of the membrane after this treatment (Figure 37).

132

A B

C D

Figure 39: SEM images of membranes after PFOA removal procedure: (A) baseline clean membrane, (B) after PFOA filtration, (C) after UV treatment of PFOA-fouled membrane surface, and (D) after oxygen treatment of PFOA-fouled membrane surface. After each treatment, the chemical composition of the membrane surface and pores were studied via depth profile analysis using XPS. Figure 40 shows the elemental fluorine depth

profile for the membranes after filtration of PFOA (40A), the membranes after filtration of

PFOA and irradiation with UV (40B), and the membranes after filtration of PFOA and

oxygenation (40C). In XPS depth profiling, the first point for all membranes, at 0 seconds

etch time, shows the percentage of fluorine on the surface of the membrane, and subsequent

values show the percentages as more of the membrane was etched; therefore, showing

percentages in membrane pores. Other elements were carbon and oxygen; however, only

fluorine is shown here since that is the element only present in PFOA, and not on the

133

membranes; thus, this was the element tracked to monitor presence/removal of PFOA.

Figure 40A, permeate after filtration, shows that all the fluorine was on the surface of the

membranes with minimal amounts inside the pore structure. This directly agrees with the

fact that the membrane pore sizes were smaller than the size of PFOA, and with Figure

39(B) that shows the high accumulation of PFOA on the membrane surface after filtration.

It is important to note that the two treatments were not performed after reverse flow

filtration but before it, so a direct comparison against Figure 40A is possible to show if

removal occurred. Regarding UV treatment, Figure 40B shows that the amount of fluorine

on the surface of the membranes was approximately half of that accumulated on the surface

(40A), which indicates that UV irradiation was effective at the removal of fluorine from the membrane surface in agreement with Figure 39C. Furthermore, the presence of fluorine within the pores might indicate some destruction of PFOA into smaller compounds that were able to travel inside the membrane pores. On the other hand, oxygenation did not impact the amount of fluorine present on the membrane surface as compared to reverse flow filtration and UV irradiation; however, the presence of fluorine inside the membrane pore structure suggests that some potential degradation of PFOA into smaller fluorine compounds might have occurred. Therefore, of all the treatment methods, the oxygenated membrane had the highest percentage of fluorine on its surface at 0.6%, followed by the membrane that was not treated after filtration at 0.5%, and lastly the UV irradiated membrane at 0.23%. This supports the contact angle findings (Figure 37) and the SEM images (Figure 39) that the oxygenated membranes had more perfluorinated groups present

134

Figure 40: Depth atomic profile showing the percentage of fluorine on the membrane surfaces and within their pores after (A) filtration, (B) UV irradiation, and (C) oxygenation. on their surface after the treatment. AFM images of the membranes were taken to study the impact of the different treatments on the membrane surface roughness. Figure 41(A-D) shows the images of plain/clean membrane, the membrane after filtration of PFOA, the membrane after filtration of PFOA and irradiation with UV, the membrane after filtration of PFOA and oxygenation. The average root mean square values for each membrane were 73.7±8.4 nm, 59.9±13.7 nm,

26.03±2.8 nm, 35.8± .69 nm, respectively. The UV irradiated membranes were the smoothest, while the plain membranes were the roughest. From the SEM images of the

135

membrane, it was observed that the UV membranes were the least fouled membranes, and

this correlated with the roughness observed as these were the smoothest membranes. The

oxygenated membranes were the second smoothest membranes because of the mineralization of the organic acid after this treatment. The particles were much smaller than the particles seen on the surface of the membrane after filtration and this may be why it had a lower roughness value than the filtration membrane.

A B

C D

Figure 41: AFM images of membrane surface after treatment: (A) plain/clean membrane, (B) the membrane after filtration of PFOA, (C) the membrane after filtration of PFOA and irradiation with UV, and (D) the membrane after filtration of PFOA and oxygenation.

136

6.3.5 Proposed Reaction Pathway Technologies that can potentially mineralize perflouororganics rather than transfer the fate

of the contaminants from one phase to the other are highly desirable. The proposed

degradation pathways after UV and aerobic oxidation treatments are shown in Figure

42(A), pathway for the UV photocatalytic degradation of PFOA and Figure 42(B), pathway for the liquid aerobic oxidation degradation of PFOA [337-339].

A B Figure 42: Possible pathways for the degradation of PFOA after (A) UV photocatalysis and (B) liquid aerobic oxidation [337].

For the UV treatment, degradation is hypothesized to have been initiated by the scission of the C-C bonds in PFOA [337, 338], as shown in Figure 42A. This reaction then potentially led to the formation of the perfluoro heptyl radicals. These radicals are further broken down to form an unstable perfluorinated alcohol intermediate (C7F15OH), which is quickly

hydrolyzed to a perfluorinated carboxylic acid, C6F13COOH, a shorter-chained perfluorinated compound and the reaction continues until mineralization occurs[340].

Thus, perfluorooctanoic acid can be degraded via UV photocatalysis by a stepwise loss of a CF2 group[337]. The extent of the degradation was not determined in this study, and since 137

there was no fluoride ions measured after reverse flow filtration, our data do not suggest that mineralization was achieved.

The combined system of photocatalyst and oxidation can produce a synergistic effect during the degradation of perfluoro organics[339]. The degradation process theoretically begins by the decarboxylation of PFOA to produce a perfluoro carboxylic radicals[337], which are broken down leading to the formation of perfluoro heptyl radicals[339] and then the cycle continues by a stepwise loss of a CF2 group until mineralization occurs (Figure

42B). The UV pathway is potentially shorter, which explains why a higher amount of adsorbed PFOA was removed, as seen in Figure 38, under the same time duration as the oxygenation treatment. This could be associated with phosphorene’s stronger interaction with UV as compared to visible light[216].

6.4. Conclusions

In this study, we demonstrated the successful removal of a persistent contaminant, perfluorooctanoic acid (PFOA) using nanohybrid membranes made of SPEEK and phosphorene. The membranes achieved nearly complete rejection of PFOA at 99%, and the flux recovery after reverse-flow filtration was 84%, indicating the membranes were not fouled by PFOA. After filtration, the membranes were subjected to two treatments to destroy the fouled PFOA that accumulated on the membrane surface. The first was UV photolysis that removed 98.4% of the adsorbed PFOA, while the second treatment was liquid aerobic oxygenation that led to a 96.6% removal. After treatment, the UV-treated membranes became smooth, hydrophilic and showed a minimal amount of fluorine left on

138

the surface. Conversely, the oxygenated membranes became more hydrophobic and displayed a high amount of fluorine on the surface after treatment. The results from this study further confirms the photocatalytic characteristic of phosphorene. Given that PFOA is a persistent contaminant, this research has thus provided another avenue for the treatment

of contaminated waters. This highlights the need for research into the scaleup of these dual

functional membranes that exhibit very high rejection and removal of perfluorooctanoic

acid.

139

CHAPTER 7. Investigation of the Effect of an Applied Potential as a Biofouling Control Technique

7.1. Introduction

While membranes may offer an enhanced rejection of contaminants, such as PFAS

compounds, they are plagued by fouling, which is the accumulation of suspended/dissolved

substances on the external surface or within the pores of the membrane and at the pore

walls[46]. It leads to a reduction in the membrane performance, decline of the membrane

lifespan and, ultimately, increase in the operation costs. Biofouling is the process of

microbial adhesion and proliferation on membranes; that is, it is the formation of biofilms

to an unacceptable degree of fouling that increases operational costs[66]. For a biofilm to

form, a source of nutrient and the microorganism that depends on the nutrient must be

present. Prevention of biofouling involves reducing the concentration of microorganisms

and/or reducing the concentration of nutrients by pretreatment, and/or performing

preventive/curative cleanings. A number of studies [67-69] have identified some trends with respect to short-term cell adhesion and biofilm growth with controlled bacterial

strains. Generally, surface roughness and hydrophobicity are key predictors of cell

adhesion, with neutral, smooth hydrophilic surfaces providing the lowest propensity to

biofouling[68]. On a conductive surface over which a field is applied, adhesion of bacterial cells can be prevented. When a positive charge is applied, it stimulates an oxidizing environment for the bacteria, thus increasing bacterial surface mobility and preventing bacteria from adhering to the surface. Conversely, a negative charge produces a repulsive electrostatic force between the like charged bacteria and the surface. Thus, applying

140

alternating charges to a surface efficiently prevent bacteria from forming a biofilm [180].

Phosphorene possesses ambi-polar transport characteristics (where both positively and negatively charged carriers conduct current under certain voltage bias conditions [237,

341]). Therefore, it is hypothesized that it can be used to modify polymeric membranes as an anti-microbial additive.

7.2. Materials and Methods

Black phosphorus used for the synthesis of phosphorene was purchased from Smart

Elements (Vienna, Austria) and the ultrasonicator model P70H was purchased from

Elmasonic P, Singen, Germany. For the biofouling experiments, the bacterial strain,

7.2.1. Preparation of phosphorene

Phosphorene was synthesized by chemically exfoliating black phosphorus according to previously described techniques [22, 216]. In summary, NMP and NaOH with a volume ratio of 1:1 were mixed and degassed on an ultrasonicator (P70H, Elma Elmasonic P,

141

7.2.3 Sulfonation of poly ether ether ketone

Poly ether ether ketone was sulfonated as previously described [216]. Briefly, PEEK

pellets were oven dried at 60˚ C overnight, after drying the pellets were dissolved in

concentrated sulfuric acid solution (98%) for three days until a homogenous solution was

formed at 25 ˚ C. The solution was gradually added into an ice water bath which was

vigorously stirred to precipitate SPEEK (sulfonated poly ether ether ketone) polymer.

SPEEK was washed in deionized water until a pH of 7 was achieved. Then it was oven

dried at 60˚ C and stored for usage.

7.2.4 Membrane preparation

The blended polymer dope solution was prepared by dissolving PSf and SPEEK (95/5%)

into NMP. Exfoliated black phosphorus was added to the solution (0.5% wt./vol) and

sealed with parafilm to prevent air bubbles from being trapped inside the solution and

affecting the homogeneous mixing of the solvent and the solute. The blended solution was

placed on a magnetic stirrer and heated at 65 °C. It was degassed in a sonicator to remove

air bubbles for 1 h. The blended solution was spread on a glass plate with a doctor blade at a wet thickness of 0.250 mm and exposed to air for 12 s. A clean glass mirror was used as a surface, which provided optimum hydrophobicity to the membranes and helped the detachment of polymer films during phase inversion [227]. The glass plate and dope solution were immersed in a coagulation bath of deionized water and the membrane was formed via the process of phase inversion. The membranes formed were subsequently washed thoroughly with deionized water to remove residual solvent and kept in deionized water before testing. The thickness of the membrane was maintained at approximately 150

142

microns. By physical mixing between the blended membrane polymer dope and phosphorene, phosphorene nanoparticles were incorporated into the dope solution.

7.2.5 Biofouling studies

To study the antimicrobial properties of phosphorene, fouling studies were done using

Serratia marcescens subsp. marcescens Bizio (ATCC 13880). Serratia marcescens subsp. marcescens was selected to investigate the inhibitory effect of different phosphorene modified membranes on bacterial growth. BactoTM tryptic soy broth (Becton, Dickinson, and Company) was prepared based on the manufacture’s direction, then autoclaved to remove all possible bacterial contamination, and used as a growth media to culture Serratia marcescens. Bacterial solutions were prepared by overnight growth of Serratia marcescens at 27℃ in tryptic soy broth. The number of bacteria was counted after serial dilution on tryptic soy agar was 9.5 × 108 CFU/mL. Assessing the bacterial growth in the presence of different membranes was investigated on DifcoTM tryptic soy Agar (Becton, Dickinson, and

Company). Agar solutions were prepared and autoclaved to remove all bacteria. Then, agar plates were prepared aseptically by adding autoclaved agar solution into each plate under a laminar flow hood.

To investigate the specific role of electrical potential on bacterial detachment and inactivation a voltage was applied through the membrane, while the bacteria solution was filtered through the membrane. The filtration experimental setup consisted of a custom built cross-flow filtration cell (Sterlitech CF016A, Kent, WA) designed with built-in insulated titanium electrodes capable of delivering an electric charge to the membrane thin film surface (effective membrane surface area was 21.6 cm2). The electrodes were

143

connected to a voltage generator (Circuit Specialists CS15003X5, Tempe, AZ). During operation, a peristaltic pump (Varian Prostar 210, Santa Clara, CA) was used to deliver a pressurized feed stream at 4.13 bar over the membrane. Experiments were done under no charge, and then alternated positive and negative signal at 1.5V for 1 minute each. This

was done for thirty minutes. This was done on unmodified and phosphorene-modified

membranes. After filtration, the membranes were placed on an agar plate and left for 3

days. One agar plate was considered as a negative control to verify negative bacterial

growth on the prepared agar under sterile condition. Membrane sterilization was done by

rinsing the membranes with alcohol. To verify the membrane sterilization process, one

negative control plate was considered for each membrane by laying a sterile membrane

[round, 21.6cm2] on the prepared sterile agar plate. Then the negative control was

incubated for 24 hours at 27℃. The negative growth of bacteria on the membrane verified

the process of membrane sterilization with alcohol. Three positive controls were prepared

by adding 10 ml of Serratia marcescens to the top of the tryptic soy agar plate with sterile

membrane placed on top and then incubated for 24 hours at 27℃. Figure 42 shows a

schematic of the experimental setup. Temperature was measured during the experiments

and it remained constant at 28˚C.

144

Figure 43: Experimental set for biofouling study Bacterial growth was quantified using a technique extensively described previously [280].

In summary, pictures were taken of each membrane and the colors encoded into the RGB code model. For each plate, nine points were chosen to calculate the average value.

Equation 1 was used to estimate the color difference (CD) of each plate.

CD = ( (Ri - Ro)2 + (Gi – Go)2 + (Bi -Bo)2)1/2 (1) Where the negative control groups are denoted as O, while i denoted the remaining experimental groups; and R, G and B represent the colors red, green, and blue, respectively.

The reference object was the negative control group, while the difference between the values of the positive and negative control was assigned as 1. The CD values between the remaining groups and the negative control were normalized and hence the antimicrobial effect of the membranes could be estimated.

145

7.3. Results and Discussion

Figure 43 shows the images of the (A) negative control and (B) positive control, displaying

no growth on the membrane and a pinkish hue that indicates full microbial growth,

respectively. Figure 44 shows the images of (A) phosphorene-modified membranes under no voltage and (B) phosphorene membranes under alternating potential, where both membranes visually showed the pinkish microbial growth. Finally, Figure 45 shows the images of the SPEEK-membranes (A) under no voltage and (B) under an alternating potential. Under no voltage, the pink biofilm on the membrane surface in contact with the

agar was like the control membrane and to the phosphorene membranes; on the other hand,

under voltage (Figure 45B), the SPEEK membranes visually showed a decrease on the

surface biofilm. The color difference was calculated from the RGB values of each

membrane, and results are shown in Table 4. The values were normalized for comparison,

with the negative control being set at 0% and the positive control at 100%. The SPEEK

membrane displayed bacterial growth of 44% under an alternating potential, while under

no voltage, the bacterial growth was 60%. For the phosphorene-modified membranes,

(A) (B) Figure 44: Images of (A) Negative control (B) Positive control

146

under no voltage, bacterial growth was 65%, and under an alternating potential, the bacterial growth was 63%.

(A) (B)

Figure 45: Images of (A) Phosphorene membrane under no voltage and (B) phosphorene membrane under alternating potential

(A) (B)

Figure 46: Image of (A) SPEEK membranes under no voltage and (B) SPEEK membranes under an alternating potential

147

Table 4: Color difference values of the membranes Membrane R G B CD Normalized CD Negative 90 104 115 0 0% Control

Positive 241 231 229 229.5 100% Control

Phosphorene- 191 187 186 148.8 65% No voltage Phosphorene- 185 187 186 144.7 63% voltage PSf-SPEEK- 181 180 184 137.2 60% No Voltage PSf-SPEEK- 163 165 164 101.8 44% voltage

Two mechanisms are likely responsible for the microbial accumulation, hydrophobicity,

and charge. First, as previously reported [216], SPEEK membranes displayed an average

hydrophilicity as measured by contact angle of 48.3° ± 0.67°, while phosphorene- membranes had an average contact angle of 81.5° ± 0.64°. This shows that SPEEK

membranes were more hydrophilic, while phosphorene membranes had a more

hydrophobic nature that is associated with the presence of the more hydrophobic

phosphorene [237]. The switch from a more hydrophilic to a more hydrophobic membrane supports a stronger interaction with hydrophobic bacteria, which makes the biofouling less reversible as compared to SPEEK membranes. The second mechanism addresses the membrane surface charge, as shown in Figure 46. It was observed that both SPEEK

148

membranes and phosphorene membranes were negatively charged in both acidic and basic mediums. At a pH of approximately 6, the zeta potential of SPEEK was −61 ± 4.6 mV while that of the phosphorene membrane was −44 ± 7 mV, which was possibly due to the phosphorene nanoparticles masking some of the sulfonic sites (the source of the negative charge of the membranes). Sulfonated poly ether ether ketone is a conductive material

[342] and is more negatively charged than phosphorene as seen in Figure 46 [216].

Applying an alternating potential leads to variations in the pH environment, which creates an inconducive environment for bacteria[343]. Regardless of pH environment, the SPEEK membranes were always more negatively charged. Therefore, it is hypothesized that a combination of conductivity and charge repulsions on the unmodified membrane, enhanced its bacterial inhibition ability as compared to the modified membrane.

(A) (B)

Figure 47: Surface charge of (A) SPEEK membrane and (B) phosphorene-modified membrane

149

7.4 Conclusions

An alternating potential on the surface of membranes had been proposed to hinder bacteria growth. In the case of the SPEEK membrane, without voltage, the biofilm covered approximately 60% of the membrane surface, and under voltage, that decreased to 44%.

On the other hand, the presence of an alternating voltage did not impact the microbial surface coverage on the phosphorene membranes. It is proposed that because phosphorene membranes became more hydrophobic and less charged as compared to SPEEK membranes, microbial growth adhered more strongly to the phosphorene membranes.

Therefore, the alternating voltage was not effective in desorbing the strongly adsorbed biofilm layer from the phosphorene membranes. On the other hand, the employment of an alternating current on the more hydrophilic and more negatively charged SPEEK membranes was more effective at desorbing some of the attached biofilm from the membrane surface.

150

CHAPTER 8. Conclusions and Recommendations

8.1. Conclusions

The principal goals of this project were to show that phosphorene possesses catalytic properties to destroy organic compounds, such as dyes and PFAS compounds, and to investigate the polymer evolution of adding phosphorene to a polymeric membrane, and then show electrically conductive materials are anti-microbial. Objective one focused on a proof of concept that phosphorene could be exfoliated and stabilized on a polymeric membrane. Phosphorene was successfully chemically exfoliated from black phosphorus using a basic solvent mixture that enhanced its stability in the solvent media. As a result of this success, objective two centered on the immobilization of phosphorene and synthesis of a nanocomposite polymeric membrane to investigate the evolution in the polymer backbone because of the immobilization of phosphorene. Objectives three and five involved the study of the photocatalytic properties of phosphorene using a common organic dye, methylene blue, and a persistent organic contaminant, perfluorooctanoic acid. Finally, objective four more generally studied the potential of electroconductive surfaces in controlling microbial fouling, or biofouling.

First, the liquid exfoliation of phosphorene was performed in a mixture of sodium hydroxide and N-methyl pyrrolidinone (NMP). The exfoliated phosphorene suspension was studied using Raman spectroscopy and results verified the synthesis of phosphorene.

Raman bands were observed at 463 cm-1, 436 cm-1, and 359 cm-1, assigned to the one out-

of-plane mode A1g and two in-plane modes, B2g and A2g (A1g, B2g, and A2g represent

vibrational modes) of few-layer phosphorene corresponding to observed values from the

151

literature. The average hydrodynamic diameter of the phosphorene nanoparticles after

exfoliation was found to be 1.87 nm. The nanoparticles did not agglomerate in basic NMP

but agglomerated in water because the isoelectric point of phosphorene was closer to water.

Next, a nanocomposite membrane was synthesized using a polymeric blend of polysulfone

(PSf), sulfonated poly ether ether ketone(SPEEK) and phosphorene. Energy dispersive X-

ray spectroscopy (EDX) and Fourier-Transform Infrared Spectroscopy (FTIR) studies

confirmed the addition of phosphorene in the membrane. The pore diameter of the

phosphorene-modified membranes averaged 0.0024 microns (with smallest and largest

detected pores being 0.0022 and 0.0078 microns) implying that the membranes were

nanofiltration membranes. The membranes were less negatively charged than their

unmodified counterparts because of phosphorene masking the sulfonic groups that impacted the overall negative charge of the membrane. The membranes were also hydrophobic; phosphorene itself is very hydrophobic. The phosphorene modified

membranes were slightly rougher than the unmodified membranes with average surface

roughness (Sa), root mean square roughness (Sq) and mean roughness depth (Sz) values of

0.45 microns, 0.61 microns and 6.46 microns respectively because of the tendency for

phosphorene to agglomerate in water. The stability of phosphorene within the membrane

was investigated through leaching studies in acidic, neutral, and basic environments.

Generally, the nanoparticles seemed to be stable under all three conditions, with less than

a 1% loss in amount of phosphorene. Under the basic medium though, irrespective of the

initial concentration of phosphorene, the loss of phosphorene was highest, as compared to

other media. This could be as result of the pH of the basic media being too far from 3.0 the

isoelectric point of phosphorene, thus leading to the lesser aggregation and more detectable

152

free phosphorene. In terms of structural changes, the phosphorene membranes acted as pore formers and impacted longer finger-like pores on the membrane.

To investigate the catalytic properties of phosphorene membranes and their ability to impact a self-cleaning properties on the membrane was studied with methylene blue under

UV irradiation. It was determined that for the SPEEK and phosphorene membranes, the recovered flux values were 17 ± 6.3 (or 45% of the initial pure water flux) and 70 ± 5.8

LMH (or 85% of the pure water initial flux, or a flux value similar to that at the start of

MB filtration). Only after UV irradiation was the flux of phosphorene membranes higher and different as compared to SPEEK membrane This showed that the membranes could become self-cleaning under the intermittent application of UV irradiation. This was verified by performing experiments using phosphorene membranes operated with and without UV irradiation. Phosphorene led to a 70% reduction in dye fouling after irradiation.

In this study, we demonstrated the successful mineralization of a persistent contaminant, perfluorooctanoic acid (PFOA) using nanohybrid membranes made of SPEEK and phosphorene. The membranes achieved nearly complete rejection of PFOA at 99%, and the flux recovery after reverse-flow filtration was 84%, indicating the membranes were not fouled by PFOA. After filtration, the membranes were subjected to two treatments to destroy PFOA that accumulated on the membrane surface. The first was UV photolysis that removed 99% of the adsorbed PFOA, while the second treatment was by liquid aerobic oxygenation that led to a 97% removal. After treatment, the UV-treated membranes became smooth, hydrophilic, and showed a minimal amount of fluorine left on the surface.

Conversely, the oxygenated membranes became more hydrophobic and displayed a high amount of fluorine on the surface after treatment. The results from this study further 153

confirms the photocatalytic characteristic of phosphorene. Given that PFOA is a persistent

contaminant, this research has thus provided another avenue for the treatment of

contaminated waters. This highlights the need for research into the scaleup of these dual

functional membranes that exhibit very high rejection and removal of perfluorooctanoic

acid.

Finally, SPEEK and phosphorene membranes antimicrobial properties were investigated by applying an alternating electrical potential during the filtration of Serratia Marcescens.

The SPEEK membranes displayed an inhibition of bacterial growth by 56%, while the phosphorene modified membranes showed a lower bacterial growth inhibition of 37%. The

SPEEK membranes were more negatively charged as compared to phosphorene membranes; thus, it is likely that a combination of conductivity and charge repulsions, enhanced its bacterial inhibition ability as compared to the phosphorene membranes.

Applying an alternating potential led to variations in the pH environment that created an

unconducive environment for the bacteria. Regardless of pH environment, the SPEEK

membranes were always more negatively charged.

Overall, phosphorene-based membranes open a new field for research in membrane science

since phosphorene nanoparticles synthesized were found to be stable within the membrane

structure. While not ideal to control microbial accumulation on surfaces via alternating electric potentials, phosphorene membranes were found to provide membranes with a high removal of accumulated organic fouling after filtration under UV irradiation.

8.2. Recommendations

For future studies, here are some recommendations

154

1. Understanding the reaction mechanism and identification of the byproducts of

membrane photocatalytic reaction studies utilizing phosphorene. Since this is a

novel study, no information is available on the exact reaction pathway for

degradation of compounds with phosphorene. This study showed that phosphorene

could lead to the breakdown of organic molecules, but it did not clarify whether

phosphorene also caused toxification. Hence, the possible byproducts that remain

as retentate on the membrane surface must be analyzed to prevent the creation of

toxic waste after photocatalysis. Future studies should be focused on accessing

reaction pathway, mechanisms and byproducts after membrane photocatalytic

processes involving phosphorene.

2. This dissertation addressed the stability of phosphorene, by applying a technique

that increased stability from seconds to seven days after incorporating within the

membrane. Since studies have shown that phosphorene can form heterostructures

with polymers that act as a shell to increase ambient stability of phosphorene, future

studies can investigate immobilizing phosphorene chemically with a reaction in the

polymer to permanently address stability.

3. In this study, microscopic studies showed that the quantity of phosphorene was

higher within the pores than on the surface. If phosphorene is to be used for its

conductive properties, the need to maximize the amount of phosphorene on the

surface of the membrane that encounters biofilm growth is paramount. Hence,

future studies can be directed towards developing a technique to ensure availability

of phosphorene on the membrane surface.

155

4. The membranes created with phosphorene had an uneven pore size distribution.

This stemmed largely from the uneven size distribution of exfoliated phosphorene.

Future studies can be focused on preparation of evenly sized phosphorene

nanoparticles so that after immobilization into the membrane structure, it would not

create uneven pore sizes.

5. Finally, since phosphorene possesses electron mobility, these properties can also

be explored for electrodialysis applications. Future studies can be directed towards

the development of an ion exchange membrane with phosphorene where it can also

be applied towards the separation of ions to for product recovery.

156

APPENDICES

APPENDIX 1 FILTRATION DATA

Table A1. The original filtration data in Chapter 4, SPEEK membranes under UV irradiation. All the dead-end filtration experiments were performed at room temperature, at pressure of 2.06 bar (30 psi). Sample Number Average STD (LMH) x time (h) Flux (LMH) 1 66.9728282 19.96295653 0 2 59.788142 12.8667915 0.048333333 3 54.9709953 3.966363629 0.075555556 4 53.1993498 0 0.103611111 5 49.4989555 4.495547336 0.133888889 Precompaction 6 45.2729418 9.748755176 0.167638889 7 43.7579603 11.89126254 0.203055556 8 39.6806609 16.94806576 0.244444444 9 37.4885982 17.99955938 0.289444444 10 37.1993245 17.75109451 0.334722222 Sample Number Average STD (LMH) x time (h) Flux (LMH) 1 41.9396232 30.08558602 0.382638889 2 40.6000143 30.94057709 0.434444444 3 51.2098015 46.30902043 0.48375 4 54.9409299 35.71611182 0.518194444 Filtration 5 52.6135463 37.33967156 0.556111111 6 49.4747765 34.12469508 0.595694444 7 48.2204363 29.22599784 0.633611111 8 40.9143096 18.89357436 0.674444444 9 34.6678958 17.62797608 0.723888889 10 29.3602934 16.9302706 0.784861111 Sample Number Average STD (LMH) x time (h) Flux (LMH) Reverse flow 1 16.794859 6.283104893 0.880416667 filtration

157

Table A2. The original filtration data in Chapter 4, phosphorene-modified membranes under UV irradiation. All the dead-end filtration experiments were performed at room temperature, at pressure of 2.06 bar (30 psi). Sample Number Average STD (LMH) x time (h) Flux (LMH) 1 107.351695 33.61023601 0 2 125.800428 59.06267845 0.029166667 3 118.47347 47.12550725 0.043611111

Precompaction 4 106.803644 37.59769179 0.059166667 5 103.837796 37.50315027 0.075277778 6 94.2738714 32.68347155 0.09287037 7 93.4133679 32.76165853 0.110648148 8 88.809611 29.23385368 0.129074074 9 84.336559 26.76056849 0.148333333 10 82.4578407 24.89316332 0.16787037 Sample Number Average STD (LMH) x time (h) Flux (LMH) 1 68.1734561 20.27655497 0.191203704 2 59.1431034 21.50329429 0.218425926 3 51.9084387 17.16831095 0.249074074 Filtration 4 48.4750136 14.76735876 0.281574074 5 47.3738665 14.36981204 0.314814815 6 44.2376248 14.57500111 0.350740741 7 42.0730677 12.04398067 0.387962963 8 39.0595985 12.377492 0.428518519 9 36.3278517 8.512786355 0.471018519 10 30.6488946 2.709005148 0.503611111 Sample Number Average STD (LMH) x time (h) Flux (LMH) Reverse flow 1 70.3904759 5.765594875 0.524907407 filtration

158

Table A3. The original filtration data in Chapter 5, SPEEK: PSf membranes. All the dead-end filtration experiments were performed at room temperature, at pressure of 2.06 bar (30 psi).

Sample Average Flux STD (LMH) x time(h) Number (LMH) 1 99.94102 12.85841 0 2 94.0949 11.34695 0.031111 3 86.05697 6.277197 0.048519 4 81.64034 5.206395 0.066852 Precompactio 5 77.59902 3.46925 0.086111 n 6 72.65624 6.529657 0.106759 7 65.61208 2.936088 0.129537 8 59.70345 4.525441 0.15463 9 53.48409 5.9955 0.182778 10 46.63067 4.588451 0.215 Sample Average Flux STD (LMH) x time(h) Number (LMH) 1 36.5824 2.448751 0.255926 2 35.49819 2.758371 0.298148 3 33.6773 2.159583 0.342593 4 31.73728 1.776616 0.389722 Filtration 5 30.56075 1.190799 0.438611 6 29.25273 1.473096 0.489722 7 28.0631 1.105178 0.542963 8 26.5296 1.575024 0.599352 9 24.97175 3.002053 0.659722 10 23.45838 3.457348 0.724259 Sample Average Flux STD (LMH) x time (h) Number (LMH) Reverse flow 1 65.45166 9.647242 0.747407 filtration

159

Table A4. The original filtration data in Chapter 5, phosphorene membranes. All the dead-end filtration experiments were performed at room temperature, at pressure of 2.06 bar (30 psi).

Sample Average Flux STD (LMH) x time (h) Number (LMH) 1 86.75923 40.70708 0 2 67.60913 33.25218 0.048796 3 63.19583 33.34713 0.076481 4 52.2167 20.35018 0.107963 Precompaction 5 42.24353 10.92602 0.144907 6 37.46703 10.76397 0.186759 7 32.72821 8.70575 0.234352 8 31.02122 9.51196 0.285185 9 26.24509 6.354734 0.344074 10 23.73898 3.619904 0.40787 Sample Average Flux STD (LMH) x time (h) Number (LMH) 1 18.67638 7.708057 0.499722 2 17.59881 8.604127 0.604352 3 16.86802 8.606555 0.715185 4 16.20714 8.273278 0.829722 Filtration 5 14.76954 8.365057 0.957778 6 13.62421 8.818117 1.10537 7 12.49385 8.942061 1.282593 8 11.66614 8.763281 1.472593 9 9.864438 7.217822 1.697222 10 8.627122 5.98042 1.947593 Sample Average Flux STD (LMH) x time (h) Number (LMH) Reverse flow 1 29.80389 14.39896 2.006019 filtration

160

Table A5. The original filtration data in Chapter 6, phosphorene membrane. All the dead- end filtration experiments were performed at room temperature, at pressure of 2.06 bar (30 psi).

Sample Average Flux STD x time Number (LMH) (h) 1 163.7423955 55.84638 0 2 153.9889009 52.32174 0.05164 3 148.0769399 50.47436 0.079016 4 141.8842209 47.14102 0.107404 Precompaction 5 137.3961841 43.9399 0.136514 6 134.451834 43.68452 0.166346 7 132.4294158 43.16128 0.196674 8 131.6832801 41.5555 0.227004 9 129.8493406 39.71423 0.257653 10 130.2377173 40.22008 0.288248 Sample Average Flux STD x time Number (LMH) (h) 1 123.4550382 40.66458 0.321036 2 119.813208 40.96331 0.355151 3 117.5976641 38.88534 0.389755 4 114.5335889 36.28699 0.425076 Filtration 5 112.5901049 34.65417 0.460888 6 110.9584539 32.96758 0.497041 7 110.140034 31.86595 0.533319 8 108.2656931 31.55483 0.570282 9 107.6202547 30.59819 0.607334 10 105.9621011 29.38198 0.644828 Sample Average Flux STD x time Number (LMH) (h) Reverse flow 1 117.4992066 79.29763995 0.707563 filtration

161

Table A6. The original filtration data in Chapter 6, normalized flux data. All the dead-end filtration experiments were performed at room temperature, at pressure of 2.06 bar (30 psi). Sample Normalized STD Number Average Flux 1 100 0 2 94.56028 7.069928 3 91.35401 10.60019 4 87.90841 11.65367 Precompaction 5 85.51682 12.4816 6 83.52505 11.69994 7 82.17231 10.95674 8 82.00485 11.79139 9 80.99328 11.49079 10 81.18019 11.45057 Sample Normalized STD Number Average Flux 1 76.11469 6.732981 2 73.47125 4.874432 3 72.24781 3.974038 4 70.55982 3.454798 Filtration 5 69.47906 3.265807 6 68.66527 3.963993 7 68.31122 4.612404 8 67.09974 4.388098 9 66.84399 5.074843 10 65.95316 5.561407 Sample Normalized STD Number Average Flux Reverse flow filtration 1 64.39122 1.622343

162

APPENDIX 2: DYNAMIC LIGHT SCATTERING DATA

TABLE B1: RAW DATA SHOWING PHOSPHORENE NANOPARTICLE

HYDRODYNAMIC SIZE

Measurement name phosphorene in nmp

Measurement mode Particle size

Comment

Results Hydrodynamic diameter 1.871229178 Nm

Polydispersity index 28.01990354 %

Peak intensity 1 1.60917495 Nm

Peak intensity 2 596.508266 Nm

Peak intensity 3 Nm

Peak volume 1 0.706919181 Nm

Peak volume 2 Nm

Peak volume 3 Nm

Peak number 1 0.486446111 Nm

Peak number 2 Nm

Peak number 3 Nm

D10 volume 0.384520664 Nm

D50 volume 0.58175405 Nm

163

D90 volume 1.085514525 Nm

Undersize span (D90- 1.204966018

D10)/D50

Processed runs 6

Intercept (g2-1) 0.163126711

Baseline 1.037007164

Mean intensity 170.6745791 Kcps

Fit error 1.30709E-05

Diffusion coefficient 233.4102507 µm²/s

Automatic values Filter optical density 0.499408871

Focus position -0.004384041 Mm

Auto run criteria 228.60257 %

Transmittance 11.37604043 %

Angle used BackScatter

Input parameters General

Measurement cell Disposable

Measurement angle Automatic

Target temperature 25 °C

Equilibration time 0:00:30 hh:mm:ss

Analysis model General

164

Cumulant model Advanced

Quality

Mode Automatic

Max. number of runs 60

Measurement time 0:00:10 hh:mm:ss

Filter

Mode Automatic

Optical density 0 Mm

Focus

Mode Automatic

Position 0 Mm

Material

Name phosphorene

Refractive index 3.4

Absorption 1.028

Solvent

Name NMP

165

Refractive index 1.47

Viscosity 0.001 Pa.s

Additional Measurement start information

User DBLab

Time 6/6/2018 17:11

Software version 1.8.4

Computer name COE4287

Instrument

Type Litesizer 500

Serial number 82230463

Module

Type BM10

Serial number 82216535

TABLE B2: SIZE DISTRIBUTION FUNCTION FOR PHOSPHORENE NANO

PARTICLES

166

Size

distributio

n function

Particle Relative Relative Relative Undersize Undersize Undersize diameter frequency frequency frequency

Intensity Volume Number Intensity Volume Number

weighted weighted weighted weighted weighted weighted

[nm] [%] [%] [%] [%] [%] [%]

0.209474 0 0 0 0 0 0

0.227146 0 0 0 0 0 0

672

0.246310 0 0 0 0 0 0

121

0.267090 0 0 0 0 0 0

313

0.289623 0 0 0 0 0 0

646

0.314058 0 0 0 0 0 0

025

0.340553 0.088949 2.277703 8.90294278 0.088949 2.277703 8.902942

834 277 567 8 277 567 788

167

0.369284 0.230733 4.635337 14.2098711 0.319682 6.913041 23.11281

989 371 882 2 648 449 391

0.400440 0.400507 6.312451 15.1767630 0.720190 13.22549 38.28957

074 794 431 6 442 288 697

0.434223 0.600944 7.430804 14.0116515 1.321134 20.65629 52.30122

589 535 956 4 977 784 85

0.470857 0.832333 8.074389 11.9408582 2.153468 28.73068 64.24208

283 03 868 6 007 77 676

0.510581 1.092532 8.314829 9.64387446 3.246000 37.04551 73.88596

614 894 703 6 901 741 123

0.553657 1.377110 8.222189 7.47924998 4.623111 45.26770 81.36521

326 704 798 4 605 721 121

0.600367 1.679630 7.867273 5.61263990 6.302742 53.13498 86.97785

163 854 827 5 459 103 112

0.651017 1.992065 7.319750 4.09554374 8.294808 60.45473 91.07339

72 908 773 8 367 181 487

0.705941 2.305290 6.644911 2.91592833 10.60009 67.09964 93.98932

461 401 618 3 877 342 32

0.765498 2.609621 5.900643 2.03076354 13.20972 73.00028 96.02008

896 927 278 7 07 67 675

0.830080 2.895373 5.135352 1.38612566 16.10509 78.13563 97.40621

952 767 33 9 446 903 241

168

0.900111 3.153384 4.387028 0.92869939 19.25847 82.52266 98.33491

535 505 358 8 897 739 181

0.976050 3.375492 3.683333 0.61153051 22.63397 86.20600 98.94644

317 598 575 9 157 097 233

1.058395 3.554928 3.042468 0.39616442 26.18890 89.24846 99.34260

747 449 073 6 001 904 676

1.147688 3.686603 2.474526 0.25270506 29.87550 91.72299 99.59531

33 193 712 9 321 575 183

1.244514 3.767281 1.983088 0.15883139 33.64278 93.70608 99.75414

167 8 856 3 501 461 322

1.349508 3.795637 1.566834 0.09842144 37.43842 95.27291 99.85256

811 218 859 9 223 947 467

1.463361 3.772191 1.221043 0.06015478 41.21061 96.49396 99.91271

429 204 829 343 329 945

1.586819 3.699155 0.938884 0.03627633 44.90976 97.43284 99.94899

333 122 364 1 855 766 578

1.720692 3.580189 0.712457 0.02158950 48.48995 98.14530 99.97058

883 771 59 2 832 525 528

1.865860 3.420106 0.533587 0.01268124 51.91006 98.67889 99.98326

805 635 738 3 496 299 653

2.023275 3.224533 0.394379 0.00735094 55.13459 99.07327 99.99061

96 988 753 1 895 274 747

169

2.193971 2.999569 0.287577 0.00420393 58.13416 99.36085 99.99482

596 994 406 894 015 14

2.379068 2.751442 0.206761 0.00237051 60.88561 99.56761 99.99719

135 061 328 3 1 147 191

2.579780 2.486187 0.146426 0.00131663 63.37179 99.71403 99.99850

523 929 459 4 893 793 854

2.797426 2.209370 0.101974 0.00071913 65.58116 99.81601 99.99922

205 121 75 5 905 268 768

3.033433 1.925832 0.069653 0.00038524 67.50700 99.88566 99.99961

777 202 27 125 595 292

3.289352 1.639503 0.046461 0.00020153 69.14650 99.93212 99.99981

356 025 467 7 428 742 446

3.566861 1.353253 0.030045 0.00010221 70.49975 99.96217 99.99991

754 714 173 4 799 259 667

3.867783 1.068811 0.018589 4.95991E- 71.56856 99.98076 99.99996

501 018 459 05 901 205 627

4.194092 0.786729 0.010718 2.24282E- 72.35529 99.99148 99.99998

803 265 043 05 827 009 87

4.547931 0.506420 0.005403 8.8681E-06 72.86171 99.99688 99.99999

505 988 543 926 364 757

4.931622 0.226243 0.001890 2.43329E- 73.08796 99.99877 100

152 243 472 06 25 411

170

5.347683 0 0 0 73.08796 99.99877 100

232 25 411

5.798845 0 0 0 73.08796 99.99877 100

708 25 411

6.288070 0 0 0 73.08796 99.99877 100

943 25 411

6.818570 0 0 0 73.08796 99.99877 100

139 25 411

7.393825 0 0 0 73.08796 99.99877 100

414 25 411

8.017612 0 0 0 73.08796 99.99877 100

658 25 411

8.694026 0 0 0 73.08796 99.99877 100

316 25 411

9.427506 0 0 0 73.08796 99.99877 100

268 25 411

10.22286 0 0 0 73.08796 99.99877 100

697 25 411

11.08532 0 0 0 73.08796 99.99877 100

904 25 411

12.02055 0 0 0 73.08796 99.99877 100

356 25 411

171

13.03467 0 0 0 73.08796 99.99877 100

921 25 411

14.13436 0 0 0 73.08796 99.99877 100

255 25 411

15.32682 0 0 0 73.08796 99.99877 100

174 25 411

16.61988 0 0 0 73.08796 99.99877 100

39 25 411

18.02203 0 0 0 73.08796 99.99877 100

65 25 411

19.54248 0 0 0 73.08796 99.99877 100

307 25 411

21.19120 0 0 0 73.08796 99.99877 100

359 25 411

22.97902 0 0 0 73.08796 99.99877 100

25 411

24.91766 0 0 0 73.08796 99.99877 100

729 25 411

27.01987 0 0 0 73.08796 99.99877 100

042 25 411

29.29942 0 0 0 73.08796 99.99877 100

797 25 411

172

31.77130 0 0 0 73.08796 99.99877 100

259 25 411

34.45171 0 0 0 73.08796 99.99877 100

931 25 411

37.35827 0 0 0 73.08796 99.99877 100

198 25 411

40.51003 0 0 0 73.08796 99.99877 100

878 25 411

43.92770 0 0 0 73.08796 99.99877 100

745 25 411

47.63371 0 0 0 73.08796 99.99877 100

104 25 411

51.65237 0 0 0 73.08796 99.99877 100

521 25 411

56.01007 0 0 0 73.08796 99.99877 100

788 25 411

60.73542 0 0 0 73.08796 99.99877 100

236 25 411

65.85942 0 0 0 73.08796 99.99877 100

51 25 411

71.41571 0 0 0 73.08796 99.99877 100

93 25 411

173

77.44077 0 0 0 73.08796 99.99877 100

564 25 411

83.97414 0 0 0 73.08796 99.99877 100

169 25 411

91.05870 0 0 0 73.08796 99.99877 100

15 25 411

98.74095 0 0 0 73.08796 99.99877 100

706 25 411

107.0713 0 0 0 73.08796 99.99877 100

335 25 411

116.1045 0 0 0 73.08796 99.99877 100

103 25 411

125.8997 0 0 0 73.08796 99.99877 100

798 25 411

136.5214 0 0 0 73.08796 99.99877 100

367 25 411

148.0391 0 0 0 73.08796 99.99877 100

999 25 411

160.5286 0 0 0 73.08796 99.99877 100

704 25 411

174.0718 0 0 0 73.08796 99.99877 100

272 25 411

174

188.7575 0 0 0 73.08796 99.99877 100

656 25 411

204.6822 0 0 0 73.08796 99.99877 100

804 25 411

221.9504 0 0 0 73.08796 99.99877 100

993 25 411

240.6755 0 0 0 73.08796 99.99877 100

682 25 411

260.9803 0 0 0 73.08796 99.99877 100

956 25 411

282.9982 0 0 0 73.08796 99.99877 100

595 25 411

306.8736 0 0 0 73.08796 99.99877 100

818 25 411

332.7633 0.133791 6.89804E 2.8901E-15 73.22175 99.99877 100

772 533 -07 404 48

360.8372 0.921450 6.79771E 2.23368E- 74.14320 99.99878 100

819 052 -06 14 409 16

391.2796 1.580663 1.62773E 4.19482E- 75.72386 99.99879 100

687 269 -05 14 736 787

424.2903 2.104766 2.95177E 5.96605E- 77.82863 99.99882 100

57 718 -05 14 408 739

175

460.0860 2.490763 4.64695E 7.36621E- 80.31939 99.99887 100

24 276 -05 14 735 386

498.9016 2.739213 6.655E- 8.27365E- 83.05861 99.99894 100

27 154 05 14 051 041

540.9919 2.853981 8.8628E- 8.64156E- 85.91259 99.99902 100

461 965 05 14 247 904

586.6332 2.841873 0.000111 8.49333E- 88.75446 99.99914 100

557 842 067 14 631 011

636.1251 2.712182 0.000131 7.90368E- 91.46664 99.99927 100

386 375 784 14 869 189

689.7924 2.476194 0.000148 6.97428E- 93.94284 99.99942 100

521 087 273 14 278 016

747.9874 2.146677 0.000157 5.81134E- 96.08952 99.99957 100

605 361 531 14 014 769

811.0921 1.737385 0.000155 4.5095E-14 97.82690 99.99973 100

472 098 864 523 356

879.5207 1.262592 0.000138 3.14311E- 99.08949 99.99987 100

219 922 518 14 816 208

953.7223 0.736687 9.91104E 1.76379E- 99.82618 99.99997 100

395 668 -05 14 582 119

1034.184 0.173814 2.8814E- 4.02165E- 100 100 100

049 176 05 15

176

1121.433 0 0 0 100 100 100

988

1216.044 0 0 0 100 100 100

852

1318.637 0 0 0 100 100 100

654

1429.885 0 0 0 100 100 100

797

1550.519 0 0 0 100 100 100

498

1681.330 0 0 0 100 100 100

577

1823.177 0 0 0 100 100 100

1976.991 0 0 0 100 100 100

809

2143.782 0 0 0 100 100 100

638

2324.644 0 0 0 100 100 100

937

2520.765 0 0 0 100 100 100

859

177

2733.432 0 0 0 100 100 100

713

2964.041 0 0 0 100 100 100

412

3214.105 0 0 0 100 100 100

637

3485.266 0 0 0 100 100 100

772

3779.304 0 0 0 100 100 100

679

4098.149 0 0 0 100 100 100

4443.893 0 0 0 100 100 100

722

4818.807 0 0 0 100 100 100

5225.350 0 0 0 100 100 100

451

5666.192 0 0 0 100 100 100

204

6144.225 0 0 0 100 100 100

998

178

6662.589 0 0 0 100 100 100

576

7224.685 0 0 0 100 100 100

399

7834.202 0 0 0 100 100 100

982

8495.143 0 0 0 100 100 100

105

9211.844 0 0 0 100 100 100

082

9989.010 0 0 0 100 100 100

232

10831.74 0 0 0 100 100 100

276

11745.57 0 0 0 100 100 100

323

12736.49 0 0 0 100 100 100

989

13811.02 0 0 0 100 100 100

704

14976.20 0 0 0 100 100 100

772

179

16239.68 0 0 0 100 100 100

999

17609.76 0 0 0 100 100 100

716

19095.43 0 0 0 100 100 100

223

180

TABLE B3: CORRELATION FUNCTION FOR PHOSPHORENE NANOPARTICLES

Correlation function

Cumulant fit

Delay time [s] g2 Advanced

0.0000002 1.206321185 1.173913315

0.00000022 1.209364189 1.17192865

0.00000024 1.195513593 1.169972757

0.00000026 1.198396739 1.168045217

0.00000028 1.196870283 1.166145619

0.0000003 1.206521942 1.162428638

0.00000032 1.199548757 1.158818642

0.00000036 1.184803393 1.155312553

0.0000004 1.186436346 1.151907379

0.00000044 1.191904156 1.148600216

0.00000048 1.171469625 1.145388242

0.00000052 1.173321435 1.142268719

0.00000056 1.171492435 1.139238984

0.0000006 1.177696911 1.133438619

0.00000064 1.177043914 1.127967352

0.00000072 1.163847344 1.12280651

0.0000008 1.161220855 1.11793848

181

0.00000088 1.161849156 1.11334665

0.00000096 1.151959358 1.109015348

0.00000104 1.151537931 1.104929792

0.00000112 1.141091156 1.101076041

0.0000012 1.145172887 1.094012087

0.00000128 1.135874541 1.087726974

0.00000144 1.132098161 1.08213483

0.0000016 1.125747335 1.077159251

0.00000176 1.122219767 1.072732258

0.00000192 1.113760513 1.068793366

0.00000208 1.115605284 1.065288758

0.00000224 1.105072081 1.062170554

0.0000024 1.111412292 1.056927637

0.00000256 1.104266573 1.052777108

0.00000288 1.092765356 1.049491362

0.0000032 1.093848609 1.046890218

0.00000352 1.088840108 1.044831035

0.00000384 1.083563194 1.043200893

0.00000416 1.083197027 1.041910399

0.00000448 1.075740811 1.040888786

0.0000048 1.070188488 1.039439784

0.00000512 1.064834807 1.038531691

182

0.00000576 1.061659564 1.037962588

0.0000064 1.059584676 1.03760593

0.00000704 1.059909185 1.037382412

0.00000768 1.056879227 1.037242333

0.00000832 1.056558977 1.037154545

0.00000896 1.04979572 1.037099528

0.0000096 1.045935683

0.00001024 1.046321003

0.00001152 1.047895242

0.0000128 1.043262443

0.00001408 1.04273225

0.00001536 1.044302109

0.00001664 1.042416311

0.00001792 1.039531865

0.0000192 1.04223864

0.00002048 1.039365666

0.00002304 1.038995134

0.0000256 1.038352093

0.00002816 1.038529289

0.00003072 1.039007193

0.00003328 1.037451153

0.00003584 1.037200087

183

0.0000384 1.036980957

0.00004096 1.036965256

0.00004608 1.037007164

0.0000512 1.037375316

0.00005632 1.037064193

0.00006144 1.035600223

0.00006656 1.035430777

0.00007168 1.034962964

0.0000768 1.036086652

0.00008192 1.036279653

0.00009216 1.035562632

0.0001024 1.036099967

0.00011264 1.035955338

0.00012288 1.034917654

0.00013312 1.036002628

0.00014336 1.035258381

0.0001536 1.034582551

0.00016384 1.03421401

0.00018432 1.034426195

0.0002048 1.034351381

0.00022528 1.033957762

0.00024576 1.034094043

184

0.00026624 1.033177357

0.00028672 1.033389635

0.0003072 1.033101124

0.00032768 1.033043846

0.00036864 1.032212524

0.0004096 1.031805208

0.00045056 1.031411942

0.00049152 1.031384395

0.00053248 1.031076382

0.00057344 1.030393488

0.0006144 1.030119588

0.00065536 1.029767091

0.00073728 1.029214559

0.0008192 1.0282962

0.00090112 1.027775361

0.00098304 1.027136947

0.00106496 1.026568559

0.00114688 1.026074896

0.0012288 1.025508847

0.00131072 1.025065633

0.00147456 1.024006941

0.0016384 1.023076688

185

0.00180224 1.022117781

0.00196608 1.02115268

0.00212992 1.020419392

0.00229376 1.019796666

0.0024576 1.019255385

0.00262144 1.018771998

0.00294912 1.017886201

0.0032768 1.017307832

0.00360448 1.016964489

0.00393216 1.016847874

0.00425984 1.017164296

0.00458752 1.017513989

0.0049152 1.017734576

0.00524288 1.018260466

0.00589824 1.019020485

0.0065536 1.019364021

0.00720896 1.019024696

0.00786432 1.018181034

0.00851968 1.016913903

0.00917504 1.015556681

0.0098304 1.014994405

0.01048576 1.015094836

186

0.01179648 1.016466047

0.0131072 1.017659964

0.01441792 1.01654622

0.01572864 1.014522685

0.01703936 1.01399959

0.01835008 1.015330547

0.0196608 1.016628033

0.02097152 1.015283937

0.02359296 1.0131762

0.0262144 1.014734941

0.02883584 1.012821923

0.03145728 1.012883282

0.03407872 1.01347299

0.03670016 1.011530472

0.0393216 1.013110543

0.04194304 1.01184907

0.04718592 1.011173014

0.0524288 1.010248705

0.05767168 1.009931069

0.06291456 1.009278104

0.06815744 1.008609211

0.07340032 1.00817805

187

0.0786432 1.007577929

0.08388608 1.006535894

0.09437184 1.005916021

0.1048576 1.005154706

0.11534336 1.004695901

0.12582912 1.004423385

0.13631488 1.003947376

0.14680064 1.00373616

0.1572864 1.00338268

0.16777216 1.002681759

0.18874368 1.001653405

0.2097152 1.000956589

0.23068672 0.999668545

0.25165824 0.998880429

0.27262976 0.998187529

0.29360128 0.997187922

0.3145728 0.996169777

0.33554432 0.995139662

0.37748736 0.993833279

0.4194304 0.993727961

0.46137344 0.993686452

0.50331648 0.993720132

188

0.54525952 0.993337338

0.58720256 0.993010422

0.6291456 0.993199739

0.67108864 0.993631312

0.75497472 0.993719915

0.8388608 0.992393812

0.92274688 0.989729661

1.00663296 0.988083174

1.09051904 0.985923765

1.17440512 0.985350337

1.2582912 0.984488033

1.34217728 0.983857124

1.50994944 0.983921263

1.6777216 0.98374037

1.84549376 0.980498645

2.01326592 0.978346388

2.18103808 0.974433656

2.34881024 0.971508459

2.5165824 0.969779574

2.68435456 0.970309648

3.01989888 0.968677797

3.3554432 0.97179397

189

3.69098752 0.976957852

4.02653184 0.982252237

4.36207616 0.982633961

4.69762048 0.993853503

5.0331648 1.001228292

5.36870912 1.020870846

6.03979776 1.032090694

6.7108864 1.062751864

7.38197504 1.102285369

8.05306368 1.104529901

190

TABLE B4: INTENSITY TRACE FOR PHOSPHORENE NANOPARTICLES

Intensity trace

Time Intensity

[s] [kcps]

0.1 266.42

0.2 133.63

0.3 130.01

0.4 119.34

0.5 112.7

0.6 118.77

0.7 116.53

0.8 124.06

0.9 163.11

1 143.45

1.1 136.88

1.2 126.91

1.3 134.43

1.4 125.93

1.5 116.24

1.6 114.43

1.7 116.25

191

1.8 116.23

1.9 117.91

2 114.66

2.1 116.27

2.2 117.69

2.3 112.94

2.4 115.75

2.5 114.93

2.6 117.69

2.7 117.47

2.8 119.36

2.9 117.85

3 120.83

3.1 115.41

3.2 114.12

3.3 114.25

3.4 116.03

3.5 112.71

3.6 114.51

3.7 117.26

3.8 118.23

3.9 115.09

192

4 112.42

4.1 114.78

4.2 115.11

4.3 112.38

4.4 112.39

4.5 115.21

4.6 114.54

4.7 113.54

4.8 114.45

4.9 113.81

5 113.91

5.1 111.19

5.2 114.09

5.3 111.83

5.4 110.49

5.5 114.02

5.6 112.93

5.7 111.73

5.8 115.85

5.9 111.68

6 111.12

6.1 113.09

193

6.2 112.57

6.3 110.75

6.4 113.01

6.5 113.16

6.6 113.59

6.7 115.63

6.8 113.2

6.9 113.36

7 115.75

7.1 113.64

7.2 114.64

7.3 113.33

7.4 113.18

7.5 114.04

7.6 113

7.7 114.61

7.8 116.8

7.9 113.77

8 114.76

8.1 113.48

8.2 116.57

8.3 117.32

194

8.4 116.7

8.5 114.8

8.6 116.87

8.7 113.98

8.8 116.91

8.9 113.81

9 116.79

9.1 112.84

9.2 117.52

9.3 115

9.4 113.4

9.5 113.9

9.6 111.57

9.7 113.14

9.8 112.13

9.9 111.3

10 173.79

10.1 248.52

10.2 230.42

10.3 232.39

10.4 173.82

10.5 188.04

195

10.6 163.54

10.7 200.02

10.8 186.58

10.9 152.52

11 184.56

11.1 178.75

11.2 193.48

11.3 212.31

11.4 179.89

11.5 147.08

11.6 176.23

11.7 209.93

11.8 210.62

11.9 215.8

12 220.1

12.1 200.8

12.2 170.08

12.3 171.04

12.4 186.41

12.5 180.46

12.6 178.72

12.7 192.14

196

12.8 208.16

12.9 212.74

13 209.96

13.1 188.57

13.2 174.97

13.3 175.66

13.4 175.52

13.5 177.99

13.6 167.93

13.7 162.9

13.8 170.97

13.9 178.17

14 184.12

14.1 180.99

14.2 178.1

14.3 162.41

14.4 150.95

14.5 137.81

14.6 140.25

14.7 159.06

14.8 169.23

14.9 184.2

197

15 197.73

15.1 187.33

15.2 166.4

15.3 158.78

15.4 164.89

15.5 180.14

15.6 204.1

15.7 185.19

15.8 194.5

15.9 175.13

16 178.48

16.1 187.67

16.2 175.68

16.3 180.11

16.4 169.25

16.5 170.58

16.6 163.58

16.7 163.58

16.8 159.66

16.9 167.36

17 158.59

17.1 170.2

198

17.2 174.53

17.3 176.58

17.4 178.46

17.5 194.55

17.6 192.59

17.7 192.47

17.8 197.97

17.9 194.76

18 200.31

18.1 204.96

18.2 189.58

18.3 189.9

18.4 167

18.5 157.73

18.6 160.39

18.7 171.57

18.8 190.42

18.9 224.36

19 223.55

19.1 216.07

19.2 215.01

19.3 197.84

199

19.4 198

19.5 200.96

19.6 217.6

19.7 214.43

19.8 207.21

19.9 203.68

20 193.74

20.1 205.15

20.2 207.2

20.3 194.78

20.4 205.04

20.5 188.07

20.6 207.64

20.7 222.59

20.8 228.77

20.9 224.44

21 220.4

21.1 221.35

21.2 217.36

21.3 206.14

21.4 217.71

21.5 213.8

200

21.6 204.14

21.7 194.16

21.8 201.95

21.9 207.59

22 219.19

22.1 211.74

22.2 202.8

22.3 208.51

22.4 200.43

22.5 208.75

22.6 212.59

22.7 213.8

22.8 206.48

22.9 205.41

23 200.35

23.1 212.18

23.2 215.61

23.3 226.62

23.4 213.75

23.5 232.69

23.6 207.81

23.7 229.14

201

23.8 218.88

23.9 200.85

24 181.41

24.1 170.57

24.2 186.29

24.3 173.42

24.4 166.58

24.5 166.62

24.6 200.05

24.7 192.08

24.8 188.33

24.9 169.47

25 157.02

25.1 230.32

25.2 258.4

25.3 254.18

25.4 267.55

25.5 218.43

25.6 196.09

25.7 190.31

25.8 160.95

25.9 149.43

202

26 148.1

26.1 163.44

26.2 153.19

26.3 169.1

26.4 171.51

26.5 180.36

26.6 188.32

26.7 189.71

26.8 206.05

26.9 205.65

27 189.6

27.1 216.61

27.2 237.15

27.3 249.09

27.4 274

27.5 279.87

27.6 264.76

27.7 249.14

27.8 252.89

27.9 276.41

28 263.81

28.1 262.86

203

28.2 264.75

28.3 232

28.4 217.51

28.5 214.57

28.6 211.37

28.7 204.18

28.8 202.47

28.9 201.61

29 199.94

29.1 199.46

29.2 195.38

29.3 206.26

29.4 200.82

29.5 212.55

29.6 218.89

29.7 202.1

204

REFERENCES

[1] B. C. Thompson, and J. M. J. Fréchet, “Polymer–Fullerene Composite Solar Cells,” Angewandte Chemie International Edition, vol. 47, no. 1, pp. 58-77, 2008. [2] D. V. Talapin, and C. B. Murray, “PbSe Nanocrystal Solids for n- and p-Channel Thin Film Field-Effect Transistors,” Science, vol. 310, no. 5745, pp. 86-89, 2005. [3] J. Wu, M. Agrawal, H. A. Becerril, Z. Bao, Z. Liu, Y. Chen, and P. Peumans, “Organic Light- Emitting Diodes on Solution-Processed Graphene Transparent Electrodes,” ACS Nano, vol. 4, no. 1, pp. 43-48, 2010/01/26, 2010. [4] A. H. Woomer, T. W. Farnsworth, J. Hu, R. A. Wells, C. L. Donley, and S. C. Warren, “Phosphorene: Synthesis, Scale-Up, and Quantitative Optical Spectroscopy,” ACS Nano, vol. 9, no. 9, pp. 8869-8884, 2015/09/22, 2015. [5] X. Huang, C. Tan, Z. Yin, and H. Zhang, “25th Anniversary Article: Hybrid Nanostructures Based on Two-Dimensional Nanomaterials,” Advanced Materials, vol. 26, no. 14, pp. 2185-2204, 2014. [6] R. Mas-Balleste, C. Gomez-Navarro, J. Gomez-Herrero, and F. Zamora, “2D materials: to graphene and beyond,” Nanoscale, vol. 3, no. 1, pp. 20-30, 2011. [7] K. J. Koski, and Y. Cui, “The new skinny in two-dimensional nanomaterials,” Acs Nano, vol. 7, no. 5, pp. 3739-3743, 2013. [8] S. Z. Butler, S. M. Hollen, L. Cao, Y. Cui, J. A. Gupta, H. R. Gutiérrez, T. F. Heinz, S. S. Hong, J. Huang, and A. F. Ismach, “Progress, challenges, and opportunities in two- dimensional materials beyond graphene,” ACS nano, vol. 7, no. 4, pp. 2898-2926, 2013. [9] K. S. Novoselov, A. Mishchenko, A. Carvalho, and A. H. Castro Neto, “2D materials and van der Waals heterostructures,” Science, vol. 353, no. 6298, 2016. [10] L. Kou, C. Chen, and S. C. Smith, “Phosphorene: Fabrication, Properties, and Applications,” The Journal of Physical Chemistry Letters, vol. 6, no. 14, pp. 2794-2805, 2015/07/16, 2015. [11] R. Aversa, R. V. Petrescu, A. Apicella, and F. I. Petrescu, “The basic elements of life's,” 2016. [12] H. Liu, Y. Du, Y. Deng, and P. D. Ye, “Semiconducting black phosphorus: synthesis, transport properties and electronic applications,” Chemical Society Reviews, vol. 44, no. 9, pp. 2732-2743, 2015. [13] X. Ling, H. Wang, S. Huang, F. Xia, and M. S. Dresselhaus, “The renaissance of black phosphorus,” Proceedings of the National Academy of Sciences, vol. 112, no. 15, pp. 4523-4530, April 14, 2015, 2015. [14] H. Liu, A. T. Neal, Z. Zhu, Z. Luo, X. Xu, D. Tománek, and P. D. Ye, “Phosphorene: An Unexplored 2D Semiconductor with a High Hole Mobility,” ACS Nano, vol. 8, no. 4, pp. 4033-4041, 2014/04/22, 2014. [15] S. P. Koenig, R. A. Doganov, H. Schmidt, A. H. C. Neto, and B. Özyilmaz, “Electric field effect in ultrathin black phosphorus,” Applied Physics Letters, vol. 104, no. 10, pp. 103106, 2014. [16] R. A. Doganov, E. C. T. O’Farrell, S. P. Koenig, Y. Yeo, A. Ziletti, A. Carvalho, D. K. Campbell, D. F. Coker, K. Watanabe, T. Taniguchi, A. H. C. Neto, and B. Özyilmaz, “Transport properties of pristine few-layer black phosphorus by van der Waals passivation in an inert atmosphere,” vol. 6, pp. 6647, 04/10/online, 2015.

205

[17] J. D. Wood, S. A. Wells, D. Jariwala, K.-S. Chen, E. Cho, V. K. Sangwan, X. Liu, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Effective Passivation of Exfoliated Black Phosphorus Transistors against Ambient Degradation,” Nano Letters, vol. 14, no. 12, pp. 6964-6970, 2014/12/10, 2014. [18] H. Wang, X. Wang, F. Xia, L. Wang, H. Jiang, Q. Xia, M. L. Chin, M. Dubey, and S.-j. Han, “Black Phosphorus Radio-Frequency Transistors,” Nano Letters, vol. 14, no. 11, pp. 6424- 6429, 2014/11/12, 2014. [19] M. Akhtar, G. Anderson, R. Zhao, A. Alruqi, J. E. Mroczkowska, G. Sumanasekera, and J. B. Jasinski, “Recent advances in synthesis, properties, and applications of phosphorene,” npj 2D Materials and Applications, vol. 1, no. 1, pp. 5, 2017/04/11, 2017. [20] X. Han, H. M. Stewart, S. A. Shevlin, C. R. A. Catlow, and Z. X. Guo, “Strain and Orientation Modulated Bandgaps and Effective Masses of Phosphorene Nanoribbons,” Nano Letters, vol. 14, no. 8, pp. 4607-4614, 2014/08/13, 2014. [21] M. Batmunkh, M. Bat-Erdene, and J. G. Shapter, Phosphorene and Phosphorene-Based Materials - Prospects for Future Applications, 2016. [22] Z. Guo, H. Zhang, S. Lu, Z. Wang, S. Tang, J. Shao, Z. Sun, H. Xie, H. Wang, and X. F. Yu, “From black phosphorus to phosphorene: basic solvent exfoliation, evolution of Raman scattering, and applications to ultrafast photonics,” Advanced Functional Materials, vol. 25, no. 45, pp. 6996-7002, 2015. [23] L. Likai, Y. Yijun, Y. Guo Jun, G. Qingqin, O. Xuedong, W. Hua, F. Donglai, C. Xian Hui, and Z. Yuanbo, “Black phosphorus field-effect transistors,” Nature Nanotechnology, vol. 9, no. 5, pp. 372, 2014. [24] L. Li, Y. Yu, G. J. Ye, Q. Ge, X. Ou, H. Wu, D. Feng, X. H. Chen, and Y. Zhang, “Black phosphorus field-effect transistors,” Nature nanotechnology, vol. 9, no. 5, pp. 372, 2014. [25] S. Das, M. Demarteau, and A. Roelofs, “Ambipolar phosphorene field effect transistor,” ACS nano, vol. 8, no. 11, pp. 11730-11738, 2014. [26] F. Xia, H. Wang, and Y. Jia, “Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics,” Nature communications, vol. 5, pp. 4458, 2014. [27] W. Lu, H. Nan, J. Hong, Y. Chen, C. Zhu, Z. Liang, X. Ma, Z. Ni, C. Jin, and Z. Zhang, “Plasma-assisted fabrication of monolayer phosphorene and its Raman characterization,” Nano Research, vol. 7, no. 6, pp. 853-859, 2014. [28] J. N. Coleman, M. Lotya, A. O’Neill, S. D. Bergin, P. J. King, U. Khan, K. Young, A. Gaucher, S. De, and R. J. Smith, “Two-dimensional nanosheets produced by liquid exfoliation of layered materials,” Science, vol. 331, no. 6017, pp. 568-571, 2011. [29] J. N. Coleman, “Liquid exfoliation of defect-free graphene,” Accounts of chemical research, vol. 46, no. 1, pp. 14-22, 2012. [30] W. Zhang, X. Xiao, Y. Li, X. Zeng, L. Zheng, and C. Wan, “Liquid-exfoliation of layered MoS2 for enhancing photocatalytic activity of TiO2/g-C3N4 photocatalyst and DFT study,” Applied Surface Science, vol. 389, pp. 496-506, 2016. [31] J. R. Brent, N. Savjani, E. A. Lewis, S. J. Haigh, D. J. Lewis, and P. O'Brien, “Production of few-layer phosphorene by liquid exfoliation of black phosphorus,” Chemical Communications, vol. 50, no. 87, pp. 13338-13341, 2014. [32] K. R. Paton, E. Varrla, C. Backes, R. J. Smith, U. Khan, A. O’Neill, C. Boland, M. Lotya, O. M. Istrate, and P. King, “Scalable production of large quantities of defect-free few-layer graphene by shear exfoliation in liquids,” Nature materials, vol. 13, no. 6, pp. 624, 2014.

206

[33] A. Favron, E. Gaufrès, F. Fossard, A.-L. Phaneuf-L’Heureux, N. Y. Tang, P. L. Lévesque, A. Loiseau, R. Leonelli, S. Francoeur, and R. Martel, “Photooxidation and quantum confinement effects in exfoliated black phosphorus,” Nature materials, vol. 14, no. 8, pp. 826, 2015. [34] J. Kang, J. D. Wood, S. A. Wells, J.-H. Lee, X. Liu, K.-S. Chen, and M. C. Hersam, “Solvent exfoliation of electronic-grade, two-dimensional black phosphorus,” ACS nano, vol. 9, no. 4, pp. 3596-3604, 2015. [35] D. Hanlon, C. Backes, E. Doherty, C. S. Cucinotta, N. C. Berner, C. Boland, K. Lee, A. Harvey, P. Lynch, and Z. Gholamvand, “Liquid exfoliation of solvent-stabilized few-layer black phosphorus for applications beyond electronics,” Nature communications, vol. 6, pp. 8563, 2015. [36] M. Batmunkh, M. Bat‐Erdene, and J. G. Shapter, “Phosphorene and Phosphorene‐Based Materials–Prospects for Future Applications,” Advanced Materials, vol. 28, no. 39, pp. 8586-8617, 2016. [37] M. M. Pendergast, and E. M. V. Hoek, “A review of water treatment membrane nanotechnologies,” Energy & Environmental Science, vol. 4, no. 6, pp. 1946-1971, 2011. [38] M. Ulbricht, “Advanced functional polymer membranes,” Polymer, vol. 47, no. 7, pp. 2217-2262, 2006/03/22/, 2006. [39] R. K. Farag, N. H. Mohamed, S. A. Abou-Alfitooh, A. S. Farag, F. Samir, S. M. Elsaeed, and R. M. Abou-Shahba, “Preparation and Characterization of Micropours Membranes Based on Modified Polyethersulfon,” EGYPTIAN JOURNAL OF CHEMISTRY, vol. 59, no. 3, pp. 269-283, 2016. [40] s. filtration. "Membrane Processes," http://synderfiltration.com/learning- center/articles/membranes/membrane-processes/. [41] H. Ivnitsky, I. Katz, D. Minz, G. Volvovic, E. Shimoni, E. Kesselman, R. Semiat, and C. G. Dosoretz, “Bacterial community composition and structure of biofilms developing on nanofiltration membranes applied to wastewater treatment,” Water Research, vol. 41, no. 17, pp. 3924-3935, 2007/09/01/, 2007. [42] N. Hilal, H. Al-Zoubi, N. A. Darwish, A. W. Mohamma, and M. Abu Arabi, “A comprehensive review of nanofiltration membranes:Treatment, pretreatment, modelling, and atomic force microscopy,” Desalination, vol. 170, no. 3, pp. 281-308, 2004/11/05/, 2004. [43] X.-L. Wang, W.-J. Shang, D.-X. Wang, L. Wu, and C.-H. Tu, “Characterization and applications of nanofiltration membranes: State of the art,” Desalination, vol. 236, no. 1, pp. 316-326, 2009/01/31/, 2009. [44] J. M. M. Peeters, J. P. Boom, M. H. V. Mulder, and H. Strathmann, “Retention measurements of nanofiltration membranes with electrolyte solutions,” Journal of Membrane Science, vol. 145, no. 2, pp. 199-209, 1998/07/08/, 1998. [45] protec. "types of membrane filtration," https://www.protecind.com/solutions/water- treatment/filtration/membrane-filtration. [46] G. Rudolph, T. Virtanen, M. Ferrando, C. Güell, F. Lipnizki, and M. Kallioinen, “A review of in situ real-time monitoring techniques for membrane fouling in the biotechnology, biorefinery and food sectors,” Journal of Membrane Science, vol. 588, pp. 117221, 2019/10/15/, 2019. [47] C. Huyskens, E. Brauns, E. Van Hoof, and H. De Wever, “A new method for the evaluation of the reversible and irreversible fouling propensity of MBR mixed liquor,” Journal of Membrane Science, vol. 323, no. 1, pp. 185-192, 2008/10/01/, 2008.

207

[48] S. Huang, R. H. Ras, and X. Tian, “Antifouling membranes for oily wastewater treatment: Interplay between wetting and membrane fouling,” Current opinion in colloid & interface science, vol. 36, pp. 90-109, 2018. [49] P. Srijaroonrat, E. Julien, and Y. Aurelle, “Unstable secondary oil/water emulsion treatment using ultrafiltration: fouling control by backflushing,” Journal of Membrane Science, vol. 159, no. 1-2, pp. 11-20, 1999. [50] B. Liao, D. Bagley, H. Kraemer, G. Leppard, and S. Liss, “A review of biofouling and its control in membrane separation bioreactors,” Water environment research, vol. 76, no. 5, pp. 425-436, 2004. [51] C. Y. Tang, T. H. Chong, and A. G. Fane, “Colloidal interactions and fouling of NF and RO membranes: A review,” Advances in Colloid and Interface Science, vol. 164, no. 1, pp. 126-143, 2011/05/11/, 2011. [52] J. Buffle, K. J. Wilkinson, S. Stoll, M. Filella, and J. Zhang, “A generalized description of aquatic colloidal interactions: the three-colloidal component approach,” Environmental Science & Technology, vol. 32, no. 19, pp. 2887-2899, 1998. [53] J. Cho, G. Amy, and J. Pellegrino, “Membrane filtration of natural organic matter: initial comparison of rejection and flux decline characteristics with ultrafiltration and nanofiltration membranes,” Water Research, vol. 33, no. 11, pp. 2517-2526, 1999. [54] S. Hong, and M. Elimelech, “Chemical and physical aspects of natural organic matter (NOM) fouling of nanofiltration membranes,” Journal of membrane science, vol. 132, no. 2, pp. 159-181, 1997. [55] M. Taniguchi, J. E. Kilduff, and G. Belfort, “Modes of natural organic matter fouling during ultrafiltration,” Environmental science & technology, vol. 37, no. 8, pp. 1676- 1683, 2003. [56] S. Chede, and I. C. Escobar, “Fouling control using temperature responsive N- isopropylacrylamide (NIPAAm) membranes,” Environmental Progress & Sustainable Energy, vol. 35, no. 2, pp. 416-427, 2016. [57] S. W. Krasner, J. P. Croué, J. Buffle, and E. M. Perdue, “Three approaches for characterizing NOM,” Journal / American Water Works Association, vol. 88, no. 6, pp. 66-79, 1996. [58] J. A. Leenheer, “Systematic approaches to comprehensive analyses of natural organic matter,” Ann. Environ. Sci., vol. 3, no. 13, pp. 1-130, 2009. [59] H. Ma, H. E. Allen, and Y. Yin, “Characterization of isolated fractions of dissolved organic matter from natural waters and a wastewater effluent,” Water Research, vol. 35, no. 4, pp. 985-996, 2001/03/01/, 2001. [60] H. Yamamura, K. Okimoto, K. Kimura, and Y. Watanabe, “Hydrophilic fraction of natural organic matter causing irreversible fouling of microfiltration and ultrafiltration membranes,” Water Research, vol. 54, pp. 123-136, 2014/05/01/, 2014. [61] J. A. Nilson, and F. A. DiGiano, “Influence of NOM composition on nanofiltration,” Journal - American Water Works Association, vol. 88, no. 5, pp. 53-66, 1996. [62] C. Combe, E. Molis, P. Lucas, R. Riley, and M. Clark, “The effect of CA membrane properties on adsorptive fouling by humic acid,” Journal of membrane science, vol. 154, no. 1, pp. 73-87, 1999. [63] W. Yuan, and A. L. Zydney, “Effects of solution environment on humic acid fouling during microfiltration,” Desalination, vol. 122, no. 1, pp. 63-76, 1999.

208

[64] A. Schäfer, U. Schwicker, M. Fischer, A. G. Fane, and T. Waite, “Microfiltration of colloids and natural organic matter,” Journal of Membrane Science, vol. 171, no. 2, pp. 151-172, 2000. [65] A. W. Zularisam, A. F. Ismail, M. R. Salim, M. Sakinah, and O. Hiroaki, “Fabrication, fouling and foulant analyses of asymmetric polysulfone (PSF) ultrafiltration membrane fouled with natural organic matter (NOM) source waters,” Journal of Membrane Science, vol. 299, no. 1, pp. 97-113, 2007/08/01/, 2007. [66] S. Creber, J. Vrouwenvelder, M. Van Loosdrecht, and M. Johns, “Chemical cleaning of biofouling in reverse osmosis membranes evaluated using magnetic resonance imaging,” Journal of Membrane Science, vol. 362, no. 1-2, pp. 202-210, 2010. [67] S. Kang, E. M. Hoek, H. Choi, and H. Shin, “Effect of membrane surface properties during the fast evaluation of cell attachment,” Separation Science and Technology, vol. 41, no. 7, pp. 1475-1487, 2006. [68] T. Knoell, J. Safarik, T. Cormack, R. Riley, S. Lin, and H. Ridgway, “Biofouling potentials of microporous polysulfone membranes containing a sulfonated polyether- ethersulfone/polyethersulfone block copolymer: correlation of membrane surface properties with bacterial attachment,” Journal of Membrane Science, vol. 157, no. 1, pp. 117-138, 1999. [69] S. S. Ghayeni, P. Beatson, R. Schneider, and A. Fane, “Adhesion of waste water bacteria to reverse osmosis membranes,” Journal of Membrane Science, vol. 138, no. 1, pp. 29- 42, 1998. [70] R. Sheikholeslami, “Composite fouling‐inorganic and biological: A review,” Environmental progress, vol. 18, no. 2, pp. 113-122, 1999. [71] C. Jarusutthirak, S. Mattaraj, and R. Jiraratananon, “Influence of inorganic scalants and natural organic matter on nanofiltration membrane fouling,” Journal of membrane science, vol. 287, no. 1, pp. 138-145, 2007. [72] S. Shirazi, C.-J. Lin, and D. Chen, “Inorganic fouling of pressure-driven membrane processes—A critical review,” Desalination, vol. 250, no. 1, pp. 236-248, 2010. [73] L. D. Tijing, Y. C. Woo, J.-S. Choi, S. Lee, S.-H. Kim, and H. K. Shon, “Fouling and its control in membrane distillation—a review,” Journal of Membrane Science, vol. 475, pp. 215- 244, 2015. [74] H. Zhou, and D. W. Smith, “Advanced technologies in water and wastewater treatment,” Journal of Environmental Engineering and Science, vol. 1, no. 4, pp. 247-264, 2002. [75] G. Pearce, “Introduction to membranes: Fouling control,” Filtration & separation, vol. 44, no. 6, pp. 30-32, 2007. [76] S. N. Jagannadh, and H. Muralidhara, “Electrokinetics methods to control membrane fouling,” Industrial & engineering chemistry research, vol. 35, no. 4, pp. 1133-1140, 1996. [77] P. L. T. Brian, “Concentration Polar zation in Reverse Osmosis Desalination with Variable Flux and Incomplete Salt Rejection,” Industrial & Engineering Chemistry Fundamentals, vol. 4, no. 4, pp. 439-445, 1965. [78] A. Michaels, “Progress in separation and purification,” ES Perry (editor), vol. 1, pp. 297, 1968. [79] W. J. Huffman, R. M. Ward, and R. C. Harshman, “Effects of forced and natural convection during ultrafiltration of protein-saline solutions and whole blood in thin channels,” Industrial & Engineering Chemistry Process Design and Development, vol. 14, no. 2, pp. 166-170, 1975.

209

[80] W. Light, "Contending with chlorine attack of reverse osmosis membranes." [81] C. Li, X. Guo, X. Wang, S. Fan, Q. Zhou, H. Shao, W. Hu, C. Li, L. Tong, and R. R. Kumar, “Membrane fouling mitigation by coupling applied electric field in membrane system: Configuration, mechanism and performance,” Electrochimica Acta, vol. 287, pp. 124- 134, 2018. [82] K. Akamatsu, W. Lu, T. Sugawara, and S.-i. Nakao, “Development of a novel fouling suppression system in membrane bioreactors using an intermittent electric field,” Water research, vol. 44, no. 3, pp. 825-830, 2010. [83] J. B. Hunter, “In focus and on the move: Prospects for electrophoresis in the food industry,” Bioseparation Processes in Foods, Marcel Dekker, New York, pp. 227-295, 1995. [84] H. Muralidhara, “Advances in solid-liquid separation,” 1986. [85] B. Van Der Bruggen, C. Vandecasteele, T. Van Gestel, W. Doyen, and R. Leysen, “A review of pressure-driven membrane processes in wastewater treatment and drinking water production,” Environmental Progress, vol. 22, no. 1, pp. 46-56, 2003. [86] D. Mosqueda-Jimenez, R. Narbaitz, T. Matsuura, G. Chowdhury, G. Pleizier, and J. Santerre, “Influence of processing conditions on the properties of ultrafiltration membranes,” Journal of Membrane Science, vol. 231, no. 1-2, pp. 209-224, 2004. [87] W. W. Lau, and Y. Jiang, “Performance of polysulfone/carboxylated polysulfone membranes,” Polymer international, vol. 33, no. 4, pp. 413-417, 1994. [88] J. Mansouri, S. Harrisson, and V. Chen, “Strategies for controlling biofouling in membrane filtration systems: challenges and opportunities,” Journal of Materials Chemistry, vol. 20, no. 22, pp. 4567-4586, 2010. [89] B. Van der Bruggen, “Chemical modification of polyethersulfone nanofiltration membranes: a review,” Journal of Applied Polymer Science, vol. 114, no. 1, pp. 630-642, 2009. [90] C. Smolders, A. Reuvers, R. Boom, and I. Wienk, “Microstructures in phase-inversion membranes. Part 1. Formation of macrovoids,” Journal of Membrane Science, vol. 73, no. 2-3, pp. 259-275, 1992. [91] Y.-F. Zhao, L.-P. Zhu, Z. Yi, B.-K. Zhu, and Y.-Y. Xu, “Improving the hydrophilicity and fouling-resistance of polysulfone ultrafiltration membranes via surface zwitterionicalization mediated by polysulfone-based triblock copolymer additive,” Journal of Membrane Science, vol. 440, pp. 40-47, 2013/08/01/, 2013. [92] A. Sotto, A. Boromand, S. Balta, J. Kim, and B. Van der Bruggen, “Doping of polyethersulfone nanofiltration membranes: antifouling effect observed at ultralow concentrations of TiO2 nanoparticles,” Journal of Materials Chemistry, vol. 21, no. 28, pp. 10311-10320, 2011. [93] M. Morra, On the molecular basis of fouling resistance, 2000. [94] J. Yoo, J. Kim, Y. Kim, and C. Kim, “Novel ultrafiltration membranes prepared from the new miscible blends of polysulfone with poly (1-vinylpyrrolidone-co-styrene) copolymers,” Journal of membrane science, vol. 216, no. 1-2, pp. 95-106, 2003. [95] P. Aerts, I. Genne, S. Kuypers, R. Leysen, I. Vankelecom, and P. Jacobs, “Polysulfone– aerosil composite membranes: Part 2. The influence of the addition of aerosil on the skin characteristics and membrane properties,” Journal of Membrane Science, vol. 178, no. 1-2, pp. 1-11, 2000. [96] I. Genne, S. Kuypers, and R. Leysen, “Effect of the addition of ZrO2 to polysulfone based UF membranes,” Journal of Membrane Science, vol. 113, no. 2, pp. 343-350, 1996.

210

[97] M. Ulbricht, and G. Belfort, “Surface modification of ultrafiltration membranes by low temperature plasma II. Graft polymerization onto polyacrylonitrile and polysulfone,” Journal of Membrane Science, vol. 111, no. 2, pp. 193-215, 1996. [98] K. Kim, K. Lee, K. Cho, and C. Park, “Surface modification of polysulfone ultrafiltration membrane by oxygen plasma treatment,” Journal of Membrane Science, vol. 199, no. 1- 2, pp. 135-145, 2002. [99] V. Thom, K. Jankova, M. Ulbricht, J. Kops, and G. Jonsson, “Synthesis of photoreactive α‐ 4‐azidobenzoyl‐ω‐methoxy‐poly (ethylene glycol) s and their end‐on photo‐grafting onto polysulfone ultrafiltration membranes,” Macromolecular Chemistry and Physics, vol. 199, no. 12, pp. 2723-2729, 1998. [100] W. Edwards, W. Leukes, P. Rose, and S. Burton, “Immobilization of polyphenol oxidase on chitosan-coated polysulphone capillary membranes for improved phenolic effluent bioremediation,” Enzyme and microbial technology, vol. 25, no. 8-9, pp. 769-773, 1999. [101] Y. Yang, H. Zhang, P. Wang, Q. Zheng, and J. Li, “The influence of nano-sized TiO2 fillers on the morphologies and properties of PSF UF membrane,” Journal of Membrane Science, vol. 288, no. 1, pp. 231-238, 2007/02/01/, 2007. [102] P. Xing, G. P. Robertson, M. D. Guiver, S. D. Mikhailenko, K. Wang, and S. Kaliaguine, “Synthesis and characterization of sulfonated poly(ether ether ketone) for proton exchange membranes,” Journal of Membrane Science, vol. 229, no. 1, pp. 95-106, 2004/02/01/, 2004. [103] Y. Fu, A. Manthiram, and M. D. Guiver, “Blend membranes based on sulfonated poly(ether ether ketone) and polysulfone bearing benzimidazole side groups for proton exchange membrane fuel cells,” Electrochemistry Communications, vol. 8, no. 8, pp. 1386-1390, 2006/08/01/, 2006. [104] G. Arthanareeswaran, D. Mohan, and M. Raajenthiren, “Preparation and performance of polysulfone-sulfonated poly(ether ether ketone) blend ultrafiltration membranes. Part I,” Applied Surface Science, vol. 253, no. 21, pp. 8705-8712, 2007/08/31/, 2007. [105] W. Richard Bowen, T. A. Doneva, and H. B. Yin, “Polysulfone — sulfonated poly(ether ether) ketone blend membranes: systematic synthesis and characterisation,” Journal of Membrane Science, vol. 181, no. 2, pp. 253-263, 2001/01/30/, 2001. [106] W. Dai, Y. Shen, Z. Li, L. Yu, J. Xi, and X. Qiu, “SPEEK/Graphene oxide nanocomposite membranes with superior cyclability for highly efficient vanadium redox flow battery,” Journal of Materials Chemistry A, vol. 2, no. 31, pp. 12423-12432, 2014. [107] T. He, M. Frank, M. H. V. Mulder, and M. Wessling, “Preparation and characterization of nanofiltration membranes by coating polyethersulfone hollow fibers with sulfonated poly(ether ether ketone) (SPEEK),” Journal of Membrane Science, vol. 307, no. 1, pp. 62- 72, 2008/01/10/, 2008. [108] M. R. Esfahani, S. A. Aktij, Z. Dabaghian, M. D. Firouzjaei, A. Rahimpour, J. Eke, I. C. Escobar, M. Abolhassani, L. F. Greenlee, and A. R. Esfahani, “Nanocomposite membranes for water separation and purification: Fabrication, modification, and applications,” Separation and Purification Technology, 2018. [109] M. A. Aroon, A. F. Ismail, T. Matsuura, and M. M. Montazer-Rahmati, “Performance studies of mixed matrix membranes for gas separation: A review,” Separation and Purification Technology, vol. 75, no. 3, pp. 229-242, 2010/11/20/, 2010. [110] R. Kumar, A. K. Pandey, S. Dhara, N. L. Misra, S. V. Ramagiri, J. R. Bellare, and A. Goswami, “Inclusion of silver nanoparticles in host poly(perfluorosulfonic) acid

211

membrane using ionic and non-ionic reductants,” Journal of Membrane Science, vol. 352, no. 1, pp. 247-254, 2010/04/15/, 2010. [111] C. P. Leo, N. H. Ahmad Kamil, M. U. M. Junaidi, S. N. M. Kamal, and A. L. Ahmad, “The potential of SAPO-44 zeolite filler in fouling mitigation of polysulfone ultrafiltration membrane,” Separation and Purification Technology, vol. 103, pp. 84-91, 2013/01/15/, 2013. [112] E. Celik, H. Park, H. Choi, and H. Choi, “Carbon nanotube blended polyethersulfone membranes for fouling control in water treatment,” Water Research, vol. 45, no. 1, pp. 274-282, 2011/01/01/, 2011. [113] L. Yan, Y. S. Li, and C. B. Xiang, “Preparation of poly (vinylidene fluoride)(pvdf) ultrafiltration membrane modified by nano-sized alumina (Al2O3) and its antifouling research,” Polymer, vol. 46, no. 18, pp. 7701-7706, 2005. [114] L.-Y. Yu, Z.-L. Xu, H.-M. Shen, and H. Yang, “Preparation and characterization of PVDF– SiO2 composite hollow fiber UF membrane by sol–gel method,” Journal of Membrane Science, vol. 337, no. 1, pp. 257-265, 2009/07/15/, 2009. [115] N. Maximous, G. Nakhla, W. Wan, and K. Wong, “Performance of a novel ZrO2/PES membrane for wastewater filtration,” Journal of Membrane Science, vol. 352, no. 1, pp. 222-230, 2010/04/15/, 2010. [116] C. P. Leo, W. P. Cathie Lee, A. L. Ahmad, and A. W. Mohammad, “Polysulfone membranes blended with ZnO nanoparticles for reducing fouling by oleic acid,” Separation and Purification Technology, vol. 89, pp. 51-56, 2012/03/22/, 2012. [117] I. Sawada, R. Fachrul, T. Ito, Y. Ohmukai, T. Maruyama, and H. Matsuyama, “Development of a hydrophilic polymer membrane containing silver nanoparticles with both organic antifouling and antibacterial properties,” Journal of Membrane Science, vol. 387-388, pp. 1-6, 2012/01/01/, 2012. [118] T.-H. Bae, and T.-M. Tak, “Effect of TiO2 nanoparticles on fouling mitigation of ultrafiltration membranes for activated sludge filtration,” Journal of Membrane Science, vol. 249, no. 1, pp. 1-8, 2005/03/01/, 2005. [119] V. Moghimifar, A. Raisi, and A. Aroujalian, “Surface modification of polyethersulfone ultrafiltration membranes by corona plasma-assisted coating TiO 2 nanoparticles,” Journal of Membrane Science, vol. 461, pp. 69-80, 2014. [120] S. S. Madaeni, and N. Ghaemi, “Characterization of self-cleaning RO membranes coated with TiO2 particles under UV irradiation,” Journal of Membrane Science, vol. 303, no. 1, pp. 221-233, 2007/10/15/, 2007. [121] H. Wu, J. Mansouri, and V. Chen, “Silica nanoparticles as carriers of antifouling ligands for PVDF ultrafiltration membranes,” Journal of Membrane Science, vol. 433, pp. 135- 151, 2013/04/15/, 2013. [122] J.-H. Li, Y.-Y. Xu, L.-P. Zhu, J.-H. Wang, and C.-H. Du, “Fabrication and characterization of a novel TiO2 nanoparticle self-assembly membrane with improved fouling resistance,” Journal of Membrane Science, vol. 326, no. 2, pp. 659-666, 2009/01/20/, 2009. [123] L. Escobar-Ferrand, D. Li, D. Lee, and C. J. Durning, “All-Nanoparticle Layer-by-Layer Surface Modification of Micro- and Ultrafiltration Membranes,” Langmuir, vol. 30, no. 19, pp. 5545-5556, 2014/05/20, 2014. [124] Z. Geng, X. Yang, C. Boo, S. Zhu, Y. Lu, W. Fan, M. Huo, M. Elimelech, and X. Yang, “Self- cleaning anti-fouling hybrid ultrafiltration membranes via side chain grafting of poly(aryl ether sulfone) and titanium dioxide,” Journal of Membrane Science, vol. 529, pp. 1-10, 2017/05/01/, 2017.

212

[125] C. D. Jones, M. Fidalgo, M. R. Wiesner, and A. R. Barron, “Alumina ultrafiltration membranes derived from carboxylate–alumoxane nanoparticles,” Journal of Membrane Science, vol. 193, no. 2, pp. 175-184, 2001/11/15/, 2001. [126] L. Huang, S. Zhao, Z. Wang, J. Wu, J. Wang, and S. Wang, “In situ immobilization of silver nanoparticles for improving permeability, antifouling and anti-bacterial properties of ultrafiltration membrane,” Journal of Membrane Science, vol. 499, pp. 269-281, 2016/02/01/, 2016. [127] C. H. Jiyun, “Guided molecular self-assembly: a review of recent efforts,” Smart Materials and Structures, vol. 12, no. 2, pp. 264, 2003. [128] T.-H. Bae, I.-C. Kim, and T.-M. Tak, “Preparation and characterization of fouling-resistant TiO2 self-assembled nanocomposite membranes,” Journal of Membrane Science, vol. 275, no. 1, pp. 1-5, 2006/04/20/, 2006. [129] S. H. Kim, S.-Y. Kwak, B.-H. Sohn, and T. H. Park, “Design of TiO2 nanoparticle self- assembled aromatic polyamide thin-film-composite (TFC) membrane as an approach to solve biofouling problem,” Journal of Membrane Science, vol. 211, no. 1, pp. 157-165, 2003/01/01/, 2003. [130] U. Voigt, V. Khrenov, K. Tauer, M. Hahn, W. Jaeger, and R. v. Klitzing, “The effect of polymer charge density and charge distribution on the formation of multilayers,” Journal of Physics: Condensed Matter, vol. 15, no. 1, pp. S213, 2003. [131] Y. J. Jo, E. Y. Choi, S. W. Kim, and C. K. Kim, “Fabrication and characterization of a novel polyethersulfone/aminated polyethersulfone ultrafiltration membrane assembled with zinc oxide nanoparticles,” Polymer, vol. 87, no. Supplement C, pp. 290-299, 2016/03/22/, 2016. [132] J. He, P. Kanjanaboos, N. L. Frazer, A. Weis, X.-M. Lin, and H. M. Jaeger, “Fabrication and Mechanical Properties of Large-Scale Freestanding Nanoparticle Membranes,” Small, vol. 6, no. 13, pp. 1449-1456, 2010. [133] J. T. O’Neal, M. J. Bolen, E. Y. Dai, and J. L. Lutkenhaus, “Hydrogen-bonded polymer nanocomposites containing discrete layers of gold nanoparticles,” Journal of Colloid and Interface Science, vol. 485, pp. 260-268, 2017/01/01/, 2017. [134] J. Dhar, and S. Patil, “Self-Assembly and Catalytic Activity of Metal Nanoparticles Immobilized in Polymer Membrane Prepared via Layer-by-Layer Approach,” ACS Applied Materials & Interfaces, vol. 4, no. 3, pp. 1803-1812, 2012/03/28, 2012. [135] M. Pan, H. Tang, S. P. Jiang, and Z. Liu, “Fabrication and Performance of Polymer Electrolyte Fuel Cells by Self-Assembly of Pt Nanoparticles,” Journal of The Electrochemical Society, vol. 152, no. 6, pp. A1081-A1088, June 1, 2005, 2005. [136] W. Ma, A. Soroush, T. Van Anh Luong, G. Brennan, M. S. Rahaman, B. Asadishad, and N. Tufenkji, “Spray- and spin-assisted layer-by-layer assembly of copper nanoparticles on thin-film composite reverse osmosis membrane for biofouling mitigation,” Water Research, vol. 99, no. Supplement C, pp. 188-199, 2016/08/01/, 2016. [137] W. Choi, J. Choi, J. Bang, and J.-H. Lee, “Layer-by-Layer Assembly of Graphene Oxide Nanosheets on Polyamide Membranes for Durable Reverse-Osmosis Applications,” ACS Applied Materials & Interfaces, vol. 5, no. 23, pp. 12510-12519, 2013/12/11, 2013. [138] Y. Shimazaki, M. Mitsuishi, S. Ito, and M. Yamamoto, “Preparation of the Layer-by-Layer Deposited Ultrathin Film Based on the Charge-Transfer Interaction,” Langmuir, vol. 13, no. 6, pp. 1385-1387, 1997/03/01, 1997. [139] D. Saeki, and H. Matsuyama, “Ultrathin and ordered stacking of silica nanoparticles via spin-assisted layer-by-layer assembly under dehydrated conditions for the fabrication of

213

ultrafiltration membranes,” Journal of Membrane Science, vol. 523, no. Supplement C, pp. 60-67, 2017/02/01/, 2017. [140] M. Hu, and B. Mi, “Layer-by-layer assembly of graphene oxide membranes via electrostatic interaction,” Journal of Membrane Science, vol. 469, pp. 80-87, 2014/11/01/, 2014. [141] E. Hao, and T. Lian, “Layer-by-Layer Assembly of CdSe Nanoparticles Based on Hydrogen Bonding,” Langmuir, vol. 16, no. 21, pp. 7879-7881, 2000/10/01, 2000. [142] M. D. Musick, C. D. Keating, M. H. Keefe, and M. J. Natan, “Stepwise Construction of Conductive Au Colloid Multilayers from Solution,” Chemistry of Materials, vol. 9, no. 7, pp. 1499-1501, 1997/07/01, 1997. [143] T. Cassagneau, T. E. Mallouk, and J. H. Fendler, “Layer-by-Layer Assembly of Thin Film Zener Diodes from Conducting Polymers and CdSe Nanoparticles,” Journal of the American Chemical Society, vol. 120, no. 31, pp. 7848-7859, 1998/08/01, 1998. [144] J. Borges, and J. F. Mano, “Molecular Interactions Driving the Layer-by-Layer Assembly of Multilayers,” Chemical Reviews, vol. 114, no. 18, pp. 8883-8942, 2014/09/24, 2014. [145] M. Hu, and B. Mi, “Enabling graphene oxide nanosheets as water separation membranes,” Environmental science & technology, vol. 47, no. 8, pp. 3715-3723, 2013. [146] S. Chede, N. M. Anaya, V. Oyanedel-Craver, S. Gorgannejad, T. A. L. Harris, J. Al-Mallahi, M. Abu-Dalo, H. A. Qdais, and I. C. Escobar, “Desalination using low biofouling nanocomposite membranes: From batch-scale to continuous-scale membrane fabrication,” Desalination, 2017/05/17/, 2017. [147] M. Zhang, K. Zhang, B. De Gusseme, and W. Verstraete, “Biogenic silver nanoparticles (bio-Ag 0) decrease biofouling of bio-Ag 0/PES nanocomposite membranes,” Water research, vol. 46, no. 7, pp. 2077-2087, 2012. [148] W. Zhao, J. Huang, B. Fang, S. Nie, N. Yi, B. Su, H. Li, and C. Zhao, “Modification of polyethersulfone membrane by blending semi-interpenetrating network polymeric nanoparticles,” Journal of membrane science, vol. 369, no. 1, pp. 258-266, 2011. [149] C. Leo, N. A. Kamil, M. Junaidi, S. Kamal, and A. Ahmad, “The potential of SAPO-44 zeolite filler in fouling mitigation of polysulfone ultrafiltration membrane,” Separation and Purification Technology, vol. 103, pp. 84-91, 2013. [150] M. M. Cortalezzi, J. Rose, A. R. Barron, and M. R. Wiesner, “Characteristics of ultrafiltration ceramic membranes derived from alumoxane nanoparticles,” Journal of Membrane Science, vol. 205, no. 1, pp. 33-43, 2002/08/01/, 2002. [151] Y. Lin, H. Li, C. Liu, W. Xing, and X. Ji, “Surface-modified Nafion membranes with mesoporous SiO2 layers via a facile dip-coating approach for direct methanol fuel cells,” Journal of Power Sources, vol. 185, no. 2, pp. 904-908, 2008/12/01/, 2008. [152] B. Rajaeian, A. Heitz, M. O. Tade, and S. Liu, “Improved separation and antifouling performance of PVA thin film nanocomposite membranes incorporated with carboxylated TiO2 nanoparticles,” Journal of Membrane Science, vol. 485, pp. 48-59, 2015/07/01/, 2015. [153] Y. Y. N. Bonggotgetsakul, R. W. Cattrall, and S. D. Kolev, “A method for the coating of a polymer inclusion membrane with a monolayer of silver nanoparticles,” Journal of Membrane Science, vol. 428, no. Supplement C, pp. 142-149, 2013/02/01/, 2013. [154] J. Yin, Y. Yang, Z. Hu, and B. Deng, “Attachment of silver nanoparticles (AgNPs) onto thin-film composite (TFC) membranes through covalent bonding to reduce membrane biofouling,” Journal of Membrane Science, vol. 441, no. Supplement C, pp. 73-82, 2013/08/15/, 2013.

214

[155] S. C. Sprick C., V. Oyandel-Craver, and I.C. Escobar, “Bio-Inspired Immobilization of Casein-Coated Silver Nanoparticles on Cellulose Acetate Membranes for Biofouling Control,” Journal of Environmental Chemical Engineering, 2018. [156] R. A. Alvarez-Puebla, G. A. Nazri, and R. F. Aroca, “Fabrication of stable bimetallic nanostructures on Nafion membranes for optical applications,” Journal of Materials Chemistry, vol. 16, no. 28, pp. 2921-2924, 2006. [157] Y. Habibi, and A. Dufresne, “Highly Filled Bionanocomposites from Functionalized Polysaccharide Nanocrystals,” Biomacromolecules, vol. 9, no. 7, pp. 1974-1980, 2008/07/01, 2008. [158] H. J. Song, and C. K. Kim, “Fabrication and properties of ultrafiltration membranes composed of polysulfone and poly(1-vinylpyrrolidone) grafted silica nanoparticles,” Journal of Membrane Science, vol. 444, pp. 318-326, 2013/10/01/, 2013. [159] S. Liang, Y. Kang, A. Tiraferri, E. P. Giannelis, X. Huang, and M. Elimelech, “Highly Hydrophilic Polyvinylidene Fluoride (PVDF) Ultrafiltration Membranes via Postfabrication Grafting of Surface-Tailored Silica Nanoparticles,” ACS Applied Materials & Interfaces, vol. 5, no. 14, pp. 6694-6703, 2013/07/24, 2013. [160] Q. Yang, H. H. Himstedt, M. Ulbricht, X. Qian, and S. Ranil Wickramasinghe, “Designing magnetic field responsive nanofiltration membranes,” Journal of Membrane Science, vol. 430, pp. 70-78, 2013/03/01/, 2013. [161] G.-f. Liu, L.-j. Huang, Y.-x. Wang, J.-g. Tang, Y. Wang, M.-m. Cheng, Y. Zhang, M. J. Kipper, L. A. Belfiore, and W. S. Ranil, “Preparation of a graphene/silver hybrid membrane as a new nanofiltration membrane,” RSC Advances, vol. 7, no. 77, pp. 49159-49165, 2017. [162] S. H. Mohamad, M. I. Idris, and H. Z. Abdullah, “Preparation of polyethersulfone ultrafiltration membrane surface coated with TiO2 nanoparticles and irradiated under UV light,” 2013. [163] H. Yang, N. Wang, L. Wang, H.-X. Liu, Q.-F. An, and S. Ji, “Vacuum-assisted assembly of ZIF-8@ GO composite membranes on ceramic tube with enhanced organic solvent nanofiltration performance,” Journal of Membrane Science, vol. 545, pp. 158-166, 2018. [164] E. Gagliano, M. Sgroi, P. P. Falciglia, F. G. Vagliasindi, and P. Roccaro, “Removal of poly- and perfluoroalkyl substances (PFAS) from water by adsorption: Role of PFAS chain length, effect of organic matter and challenges in adsorbent regeneration,” Water Research, vol. 171, pp. 115381, 2020. [165] E. R. Daly, B. P. Chan, E. A. Talbot, J. Nassif, C. Bean, S. J. Cavallo, E. Metcalf, K. Simone, and A. D. Woolf, “Per-and polyfluoroalkyl substance (PFAS) exposure assessment in a community exposed to contaminated drinking water, New Hampshire, 2015,” International journal of hygiene and environmental health, vol. 221, no. 3, pp. 569-577, 2018. [166] V. A. A. Espana, M. Mallavarapu, and R. Naidu, “Treatment technologies for aqueous perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA): A critical review with an emphasis on field testing,” Environmental Technology & Innovation, vol. 4, pp. 168- 181, 2015. [167] I. Ross, J. McDonough, J. Miles, P. Storch, P. Thelakkat Kochunarayanan, E. Kalve, J. Hurst, S. S. Dasgupta, and J. Burdick, “A review of emerging technologies for remediation of PFASs,” Remediation Journal, vol. 28, no. 2, pp. 101-126, 2018. [168] N. B. Saleh, A. Khalid, Y. Tian, C. Ayres, I. V. Sabaraya, J. Pietari, D. Hanigan, I. Chowdhury, and O. G. Apul, “Removal of poly-and per-fluoroalkyl substances from

215

aqueous systems by nano-enabled water treatment strategies,” Environmental Science: Water Research & Technology, vol. 5, no. 2, pp. 198-208, 2019. [169] H. Cao, W. Zhang, C. Wang, and Y. Liang, “Sonochemical Degradation of Poly-and Perfluoroalkyl Substances-A review,” Ultrasonics Sonochemistry, pp. 105245, 2020. [170] S. P. Sahu, M. Qanbarzadeh, M. Ateia, H. Torkzadeh, A. S. Maroli, and E. L. Cates, “Rapid degradation and mineralization of perfluorooctanoic acid by a new petitjeanite Bi3O (OH)(PO4) 2 microparticle ultraviolet photocatalyst,” Environmental Science & Technology Letters, vol. 5, no. 8, pp. 533-538, 2018. [171] N. Merino, Y. Qu, R. A. Deeb, E. L. Hawley, M. R. Hoffmann, and S. J. E. E. S. Mahendra, “Degradation and removal methods for perfluoroalkyl and polyfluoroalkyl substances in water,” vol. 33, no. 9, pp. 615-649, 2016. [172] M. B. Ahmed, M. M. Alam, J. L. Zhou, B. Xu, M. A. H. Johir, A. K. Karmakar, M. S. Rahman, J. Hossen, A. K. Hasan, and M. A. Moni, “Advanced treatment technologies efficacies and mechanism of per-and poly-fluoroalkyl substances removal from water,” Process Safety and Environmental Protection, vol. 136, pp. 1-14, 2020. [173] R. M. Rodi, “PRELIMINARY RESULTS OF PERFLUOROOCTANESULFONIC ACID REMOVAL VIA ELECTRON BEAM AT VARIOUS DOSES,” 2019. [174] J. Rishabh, N. Rekha, S. Suchithra Padmajan, L. Kyung Eun, J. Hong Ju, and K. Sang Ouk, “Phosphorene for energy and catalytic application—filling the gap between graphene and 2D metal chalcogenides,” 2D Materials, vol. 4, no. 4, pp. 042006, 2017. [175] U. Akpan, and B. Hameed, “Parameters affecting the photocatalytic degradation of dyes using TiO2-based photocatalysts: a review,” Journal of hazardous materials, vol. 170, no. 2-3, pp. 520-529, 2009. [176] F. Xia, H. Wang, D. Xiao, M. Dubey, and A. Ramasubramaniam, “Two-dimensional material nanophotonics,” Nature Photonics, vol. 8, no. 12, pp. 899, 2014. [177] J. Low, S. Cao, J. Yu, and S. Wageh, “Two-dimensional layered composite photocatalysts,” Chemical Communications, vol. 50, no. 74, pp. 10768-10777, 2014. [178] K. Novoselov, D. Jiang, F. Schedin, T. Booth, V. Khotkevich, S. Morozov, and A. Geim, “Two-dimensional atomic crystals,” Proceedings of the National Academy of Sciences of the United States of America, vol. 102, no. 30, pp. 10451-10453, 2005. [179] M. Z. Rahman, C. W. Kwong, K. Davey, and S. Z. Qiao, “2D phosphorene as a water splitting photocatalyst: fundamentals to applications,” Energy & Environmental Science, vol. 9, no. 3, pp. 709-728, 2016. [180] S. H. Hong, J. Jeong, S. Shim, H. Kang, S. Kwon, K. H. Ahn, and J. Yoon, “Effect of electric currents on bacterial detachment and inactivation,” Biotechnology and Bioengineering, vol. 100, no. 2, pp. 379-386, Jun, 2008. [181] L. Li, J. Zhang, and Y. Wang, “Sulfonated poly (ether ether ketone) membranes for direct methanol fuel cell,” Journal of Membrane Science, vol. 226, no. 1-2, pp. 159-167, 2003. [182] H.-Y. Jung, and J.-K. Park, “Blend membranes based on sulfonated poly (ether ether ketone) and poly (vinylidene fluoride) for high performance direct methanol fuel cell,” Electrochimica acta, vol. 52, no. 26, pp. 7464-7468, 2007. [183] J. da Silva Burgal, L. G. Peeva, S. Kumbharkar, and A. Livingston, “Organic solvent resistant poly(ether-ether-ketone) nanofiltration membranes,” Journal of Membrane Science, vol. 479, pp. 105-116, 2015/04/01/, 2015. [184] Y. Paik, S. A. Chae, O. H. Han, S. Y. Hwang, and H. Y. Ha, “Influence of water and degree of sulfonation on the structure and dynamics of SPEEK studied by solid-state 13C and 1H NMR,” Polymer, vol. 50, no. 12, pp. 2664-2673, 2009.

216

[185] X. Jin, M. T. Bishop, T. S. Ellis, and F. E. J. B. p. j. Karasz, “A sulphonated poly (aryl ether ketone),” vol. 17, no. 1, pp. 4-10, 1985. [186] Y. Ji, Z. Y. Tay, and S. F. Y. Li, “Highly selective sulfonated poly (ether ether ketone)/titanium oxide composite membranes for vanadium redox flow batteries,” Journal of membrane science, vol. 539, pp. 197-205, 2017. [187] S. Zaidi, and S. Mikhailenko, “Robertson. GP; Guiver, MD; Kaliaguine, S. Proton Conducting Composite Membranes from Polyether Ether Ketone and Heteropolyacids for Fuel Cell Application,” J. Membr. Sci, vol. 173, pp. 17-34, 2000. [188] J. G. Wijmans, J. Kant, M. H. V. Mulder, and C. A. Smolders, “Phase separation phenomena in solutions of polysulfone in mixtures of a solvent and a nonsolvent: relationship with membrane formation,” Polymer, vol. 26, no. 10, pp. 1539-1545, 1985/09/01/, 1985. [189] A. K. Hołda, and I. F. J. Vankelecom, “Understanding and guiding the phase inversion process for synthesis of solvent resistant nanofiltration membranes,” Journal of Applied Polymer Science, vol. 132, no. 27, pp. n/a-n/a, 2015. [190] P. Aerts, I. Genné, R. Leysen, P. A. Jacobs, and I. F. J. Vankelecom, “The role of the nature of the casting substrate on the properties of membranes prepared via immersion precipitation,” Journal of Membrane Science, vol. 283, no. 1-2, pp. 320-327, 2006. [191] J. Eke, P. Wagh, and I. C. Escobar, “Ozonation, biofiltration and the role of membrane surface charge and hydrophobicity in removal and destruction of algal toxins at basic pH values,” Separation and Purification Technology, vol. 194, pp. 56-63, 2018. [192] B. L. Xu, D. W. Liu, G. Y. Xu, X. L. Zhang, and L. C. Bi, “A measurement method for contact angle based on Hough Transformation,” Measurement, vol. 46, no. 3, pp. 1109-1114, Apr, 2013. [193] R. J. Hunter, Zeta potential in colloid science: principles and applications: Academic press, 2013. [194] W. J. Lau, A. F. Ismail, P. S. Goh, N. Hilal, and B. S. Ooi, “Characterization Methods of Thin Film Composite Nanofiltration Membranes,” Separation and Purification Reviews, vol. 44, no. 2, pp. 135-156, 2015. [195] D. C. Harris, and M. D. Bertolucci, Symmetry and spectroscopy: an introduction to vibrational and electronic spectroscopy: Courier Corporation, 1978. [196] P. Carey, Biochemical applications of Raman and resonance Raman spectroscopes: Elsevier, 2012. [197] c. s. university, “Vibrational Spectroscopy - Infrared and Raman.” [198] troglerlab, “SYMMETRY AND VIBRATIONAL SPECTROSCOPY.” [199] P.Giannozzi. "Introduction to the calculation of phonons and of vibrational spectra," http://www.tcm.phy.cam.ac.uk/~jry20/gipaw/tutorial_vib.pdf. [200] C. Lee, H. Yan, L. E. Brus, T. F. Heinz, J. Hone, and S. Ryu, “Anomalous lattice vibrations of single-and few-layer MoS2,” ACS nano, vol. 4, no. 5, pp. 2695-2700, 2010. [201] Y. Feng, J. Zhou, Y. Du, F. Miao, C.-G. Duan, B. Wang, and X. Wan, “Raman spectra of few-layer phosphorene studied from first-principles calculations,” Journal of Physics: Condensed Matter, vol. 27, no. 18, pp. 185302, 2015. [202] J. Lindau, A. S. Jönsson, and A. Bottino, “Flux reduction of ultrafiltration membranes with different cut-off due to adsorption of a low-molecular-weight hydrophobic solute- correlation between flux decline and pore size,” Journal of Membrane Science, vol. 149, no. 1, pp. 11-20, 1998/10/14/, 1998.

217

[203] M. N. Dole, P. A. Patel, S. D. Sawant, and P. S. Shedpure, “Advance applications of Fourier transform infrared spectroscopy,” Int. J. Pharm. Sci. Rev. Res, vol. 7, no. 2, pp. 159-166, 2011. [204] L.-E. Amand, and C. J. Tullin, “The Theory Behind FTIR analysis,” Dep. Of Energy Conversion, Chalmers University of Technology, Sweden, 1999. [205] C. Berthomieu, and R. Hienerwadel, “Fourier transform infrared (FTIR) spectroscopy,” Photosynthesis research, vol. 101, no. 2-3, pp. 157-170, 2009. [206] R. Davis, and L. Mauer, “Fourier transform infrared (FT-IR) spectroscopy: a rapid tool for detection and analysis of foodborne pathogenic bacteria,” Current research, technology and education topics in applied microbiology and microbial biotechnology, vol. 2, pp. 1582-1594, 2010. [207] E. M. Vrijenhoek, S. Hong, and M. Elimelech, “Influence of membrane surface properties on initial rate of colloidal fouling of reverse osmosis and nanofiltration membranes,” Journal of membrane science, vol. 188, no. 1, pp. 115-128, 2001. [208] S.-Y. Kwak, M.-O. Yeom, I. J. Roh, D. Y. Kim, and J.-J. Kim, “Correlations of chemical structure, atomic force microscopy (AFM) morphology, and reverse osmosis (RO) characteristics in aromatic polyester high-flux RO membranes,” Journal of membrane science, vol. 132, no. 2, pp. 183-191, 1997. [209] I. Koyuncu, J. Brant, A. Lüttge, and M. R. Wiesner, “A comparison of vertical scanning interferometry (VSI) and atomic force microscopy (AFM) for characterizing membrane surface topography,” Journal of membrane science, vol. 278, no. 1-2, pp. 410-417, 2006. [210] K. Boussu, B. Van der Bruggen, A. Volodin, J. Snauwaert, C. Van Haesendonck, and C. Vandecasteele, “Roughness and hydrophobicity studies of nanofiltration membranes using different modes of AFM,” Journal of colloid and interface science, vol. 286, no. 2, pp. 632-638, 2005. [211] C. Hobbs, J. Taylor, and S. Hong, “Effect of surface roughness on fouling of RO and NF membranes during filtration of a high organic surficial groundwater,” Journal of Water Supply: Research and Technology—AQUA, vol. 55, no. 7-8, pp. 559-570, 2006. [212] C. I. Weber, Methods for measuring the acute toxicity of effluents and receiving waters to freshwater and marine organisms: Environmental Monitoring Systems Laboratory, Office of Research and …, 1991. [213] O. V. Tsyusko, J. M. Unrine, D. Spurgeon, E. Blalock, D. Starnes, M. Tseng, G. Joice, and P. M. Bertsch, “Toxicogenomic responses of the model organism Caenorhabditis elegans to gold nanoparticles,” Environmental science & technology, vol. 46, no. 7, pp. 4115-4124, 2012. [214] D. L. Starnes, J. M. Unrine, C. P. Starnes, B. E. Collin, E. K. Oostveen, R. Ma, G. V. Lowry, P. M. Bertsch, and O. V. Tsyusko, “Impact of sulfidation on the bioavailability and toxicity of silver nanoparticles to Caenorhabditis elegans,” Environmental Pollution, vol. 196, pp. 239-246, 2015. [215] P. L. Williams, and D. B. Dusenbery, “Using the nematode Caenorhabditis elegans to predict mammalian acute lethality to metallic salts,” Toxicology and Industrial Health, vol. 4, no. 4, pp. 469-478, 1988. [216] J. Eke, K. Elder, and I. C. Escobar, “Self-cleaning nanocomposite membranes with phosphorene-based pore fillers for water treatment,” Membranes, vol. 8, no. 3, pp. 79, 2018. [217] B. C. Thompson, and J. M. Fréchet, “Polymer–fullerene composite solar cells,” Angewandte chemie international edition, vol. 47, no. 1, pp. 58-77, 2008.

218

[218] D. V. Talapin, and C. B. Murray, “PbSe nanocrystal solids for n-and p-channel thin film field-effect transistors,” Science, vol. 310, no. 5745, pp. 86-89, 2005. [219] J. Pei, X. Gai, J. Yang, X. Wang, Z. Yu, D.-Y. Choi, B. Luther-Davies, and Y. Lu, “Producing air-stable monolayers of phosphorene and their defect engineering,” Nature communications, vol. 7, no. 1, pp. 1-8, 2016. [220] E. S. Reich, “Phosphorene excites materials scientists,” Nature, vol. 506, no. 7486, pp. 19, 2014. [221] H. Guo, N. Lu, J. Dai, X. Wu, and X. C. Zeng, “Phosphorene nanoribbons, phosphorus nanotubes, and van der Waals multilayers,” The Journal of Physical Chemistry C, vol. 118, no. 25, pp. 14051-14059, 2014. [222] X. Liang, S.-P. Ng, N. Ding, and C.-M. L. Wu, “Enhanced hydrogen purification in nanoporous phosphorene membrane with applied electric field,” The Journal of Physical Chemistry C, vol. 122, no. 6, pp. 3497-3505, 2018. [223] Y. Zhang, F. Hao, H. Xiao, C. Liu, X. Shi, and X. Chen, “Hydrogen separation by porous phosphorene: A periodical DFT study,” International Journal of Hydrogen Energy, vol. 41, no. 48, pp. 23067-23074, 2016. [224] M. F. Haase, H. Jeon, N. Hough, J. H. Kim, K. J. Stebe, and D. Lee, “Multifunctional nanocomposite hollow fiber membranes by solvent transfer induced phase separation,” Nature communications, vol. 8, no. 1, pp. 1-7, 2017. [225] J. Zhu, J. Hou, A. Uliana, Y. Zhang, M. Tian, and B. Van der Bruggen, “The rapid emergence of two-dimensional nanomaterials for high-performance separation membranes,” Journal of Materials Chemistry A, vol. 6, no. 9, pp. 3773-3792, 2018. [226] W. R. Bowen, T. A. Doneva, and H. Yin, “The effect of sulfonated poly (ether ether ketone) additives on membrane formation and performance,” Desalination, vol. 145, no. 1-3, pp. 39-45, 2002. [227] P. Aerts, I. Genné, R. Leysen, P. Jacobs, and I. Vankelecom, “The role of the nature of the casting substrate on the properties of membranes prepared via immersion precipitation,” Journal of Membrane Science, vol. 283, no. 1-2, pp. 320-327, 2006. [228] C. M. Hansen, Hansen solubility parameters: a user's handbook: CRC press, 2007. [229] S. Zereshki, A. Figoli, S. Madaeni, S. Simone, M. Esmailinezhad, and E. Drioli, “Pervaporation separation of MeOH/MTBE mixtures with modified PEEK membrane: Effect of operating conditions,” Journal of membrane science, vol. 371, no. 1-2, pp. 1-9, 2011. [230] C. M. Hansen, Hansen solubility parameters: a user's handbook, Boca raton, Florida, USA: CRC press, 2002. [231] H.-L. Wu, C.-C. M. Ma, C.-H. Li, T.-M. Lee, C.-Y. Chen, C.-L. Chiang, and C. Wu, “Sulfonated poly (ether ether ketone)/poly (amide imide) polymer blends for proton conducting membrane,” Journal of Membrane Science, vol. 280, no. 1-2, pp. 501-508, 2006. [232] X. Dong, A. Al-Jumaily, and I. C. Escobar, “Investigation of the Use of a Bio-Derived Solvent for Non-Solvent-Induced Phase Separation (NIPS) Fabrication of Polysulfone Membranes,” Membranes, vol. 8, no. 2, pp. 23, 2018. [233] B. Xu, D. Liu, G. Xu, X. Zhang, and L. Bi, “A measurement method for contact angle based on Hough transformation,” Measurement, vol. 46, no. 3, pp. 1109-1114, 2013. [234] D. C. Harris, and M. D. Bertolucci, Symmetry and spectroscopy: an introduction to vibrational and electronic spectroscopy: Courier Corporation, 1989.

219

[235] J. Lindau, A.-S. Jönsson, and A. Bottino, “Flux reduction of ultrafiltration membranes with different cut-off due to adsorption of a low-molecular-weight hydrophobic solute- correlation between flux decline and pore size,” Journal of Membrane Science, vol. 149, no. 1, pp. 11-20, 1998. [236] S. Zhang, J. Yang, R. Xu, F. Wang, W. Li, M. Ghufran, Y.-W. Zhang, Z. Yu, G. Zhang, and Q. Qin, “Extraordinary photoluminescence and strong temperature/angle-dependent Raman responses in few-layer phosphorene,” ACS nano, vol. 8, no. 9, pp. 9590-9596, 2014. [237] W. Zhu, M. N. Yogeesh, S. Yang, S. H. Aldave, J.-S. Kim, S. Sonde, L. Tao, N. Lu, and D. Akinwande, “Flexible black phosphorus ambipolar transistors, circuits and AM demodulator,” Nano letters, vol. 15, no. 3, pp. 1883-1890, 2015. [238] J. Eke, P. A. Mills, J. R. Page, G. P. Wright, O. V. Tsyusko, and I. C. Escobar, “Nanohybrid membrane synthesis with phosphorene nanoparticles: a study of the addition, stability and toxicity,” Polymers, vol. 12, no. 7, pp. 1555, 2020. [239] D. M. Warsinger, S. Chakraborty, E. W. Tow, M. H. Plumlee, C. Bellona, S. Loutatidou, L. Karimi, A. M. Mikelonis, A. Achilli, and A. Ghassemi, “A review of polymeric membranes and processes for potable water reuse,” Progress in polymer science, vol. 81, pp. 209- 237, 2018. [240] T. Arumugham, R. G. Amimodu, N. J. Kaleekkal, and D. Rana, “Nano CuO/g-C3N4 sheets- based ultrafiltration membrane with enhanced interfacial affinity, antifouling and protein separation performances for water treatment application,” Journal of Environmental Sciences, vol. 82, pp. 57-69, 2019. [241] T.-T. Nguyen, S. Kook, C. Lee, R. W. Field, and I. S. Kim, “Critical flux-based membrane fouling control of forward osmosis: Behavior, sustainability, and reversibility,” Journal of membrane science, vol. 570, pp. 380-393, 2019. [242] P. Xu, J. E. Drewes, T.-U. Kim, C. Bellona, and G. Amy, “Effect of membrane fouling on transport of organic contaminants in NF/RO membrane applications,” Journal of Membrane Science, vol. 279, no. 1-2, pp. 165-175, 2006. [243] M. Sun, I. Zucker, D. M. Davenport, X. Zhou, J. Qu, and M. Elimelech, “Reactive, self- cleaning ultrafiltration membrane functionalized with iron oxychloride nanocatalysts,” Environmental science & technology, vol. 52, no. 15, pp. 8674-8683, 2018. [244] S. Sadki, and L. J. J. o. P. C. M. Drissi, “Tunable optical and excitonic properties of phosphorene via oxidation,” vol. 30, no. 25, pp. 255703, 2018. [245] W. Hu, L. Lin, R. Zhang, C. Yang, and J. Yang, “Highly efficient photocatalytic water splitting over edge-modified phosphorene nanoribbons,” Journal of the American Chemical Society, vol. 139, no. 43, pp. 15429-15436, 2017. [246] X. Yang, B. Sa, C. Xu, H. Zhan, M. Anpo, and Z. J. I. C. F. Sun, “Enhanced photocatalytic performance of black phosphorene by isoelectronic co-dopants,” vol. 6, no. 9, pp. 2369- 2378, 2019. [247] J. Pei, X. Gai, J. Yang, X. Wang, Z. Yu, D.-Y. Choi, B. Luther-Davies, and Y. Lu, “Producing air-stable monolayers of phosphorene and their defect engineering,” Nature communications, vol. 7, pp. 10450, 2016. [248] J. E. Fonsaca, S. H. Domingues, E. S. Orth, and A. J. Zarbin, “Air stable black phosphorous in polyaniline-based nanocomposite,” Scientific reports, vol. 7, no. 1, pp. 1-9, 2017. [249] M. Peruzzini, R. Bini, M. Bolognesi, M. Caporali, M. Ceppatelli, F. Cicogna, S. Coiai, S. Heun, A. Ienco, and I. I. Benito, “A perspective on recent advances in Phosphorene

220

functionalization and its applications in devices,” European journal of inorganic chemistry, vol. 2019, no. 11-12, pp. 1476-1494, 2019. [250] Y.-J. Lin, W.-Z. Cao, T. Ou Yang, C.-H. Feng, and C.-T. Chang, “Deciphering the effect of citric acid on arsenic adsorption with phosphorene in aqueous solution,” Sustainable Environment Research, vol. 29, no. 1, pp. 22, August 07, 2019. [251] S. Walia, S. Balendhran, T. Ahmed, M. Singh, C. El‐Badawi, M. D. Brennan, P. Weerathunge, M. N. Karim, F. Rahman, and A. Rassell, “Ambient protection of few‐layer black phosphorus via sequestration of reactive oxygen species,” Advanced Materials, vol. 29, no. 27, pp. 1700152, 2017. [252] C. R. Ryder, J. D. Wood, S. A. Wells, Y. Yang, D. Jariwala, T. J. Marks, G. C. Schatz, and M. C. Hersam, “Covalent functionalization and passivation of exfoliated black phosphorus via aryl diazonium chemistry,” Nature chemistry, vol. 8, no. 6, pp. 597, 2016. [253] S. Qiu, Y. Zhou, X. Zhou, T. Zhang, C. Wang, R. K. Yuen, W. Hu, and Y. Hu, “Air‐Stable Polyphosphazene‐Functionalized Few‐Layer Black Phosphorene for Flame Retardancy of Epoxy Resins,” Small, vol. 15, no. 10, pp. 1805175, 2019. [254] M. Zoubeik, M. Ismail, A. Salama, and A. Henni, “New developments in membrane technologies used in the treatment of produced water: A review,” Arabian Journal for Science and Engineering, vol. 43, no. 5, pp. 2093-2118, 2018. [255] J. Polte, “Fundamental growth principles of colloidal metal nanoparticles–a new perspective,” CrystEngComm, vol. 17, no. 36, pp. 6809-6830, 2015. [256] J. N. Israelachvili, Intermolecular and surface forces: Academic press, 2015. [257] E. Rabkin, G. Gottstein, and L. Shvindlerman, “Why do crystalline nanoparticles agglomerate with low misorientations?,” Scripta Materialia, vol. 65, no. 12, pp. 1101- 1104, 2011. [258] A. R. Petosa, D. P. Jaisi, I. R. Quevedo, M. Elimelech, and N. Tufenkji, “Aggregation and deposition of engineered nanomaterials in aquatic environments: role of physicochemical interactions,” Environmental science & technology, vol. 44, no. 17, pp. 6532-6549, 2010. [259] J. Zhou, J. Ralston, R. Sedev, and D. A. Beattie, “Functionalized gold nanoparticles: synthesis, structure and colloid stability,” Journal of colloid and interface science, vol. 331, no. 2, pp. 251-262, 2009. [260] J. Viota, J. De Vicente, J. Duran, and A. Delgado, “Stabilization of magnetorheological suspensions by polyacrylic acid polymers,” Journal of colloid and interface science, vol. 284, no. 2, pp. 527-541, 2005. [261] J. Lyklema, Fundamentals of interface and colloid science: Particulate colloids: Elsevier, 2005. [262] N. M. Latiff, W. Z. Teo, Z. Sofer, A. C. Fisher, and M. Pumera, “The cytotoxicity of layered black phosphorus,” Chemistry–A European Journal, vol. 21, no. 40, pp. 13991-13995, 2015. [263] Z. Xiong, X. Zhang, S. Zhang, L. Lei, W. Ma, D. Li, W. Wang, Q. Zhao, and B. Xing, “Bacterial toxicity of exfoliated black phosphorus nanosheets,” Ecotoxicology and environmental safety, vol. 161, pp. 507-514, 2018. [264] J. R. Choi, K. W. Yong, J. Y. Choi, A. Nilghaz, Y. Lin, J. Xu, and X. Lu, “Black phosphorus and its biomedical applications,” Theranostics, vol. 8, no. 4, pp. 1005, 2018. [265] X. Mu, J.-Y. Wang, X. Bai, F. Xu, H. Liu, J. Yang, Y. Jing, L. Liu, X. Xue, and H. Dai, “Black phosphorus quantum dot induced oxidative stress and toxicity in living cells and mice,” ACS applied materials & interfaces, vol. 9, no. 24, pp. 20399-20409, 2017.

221

[266] W. Zhang, Y. Chen, T. Huynh, Y. Yang, X. Yang, and R. Zhou, “Directional Extraction and Penetration of Phosphorene Nanosheets to Cell Membranes,” Nanoscale, 2020. [267] J. Choi, O. V. Tsyusko, J. M. Unrine, N. Chatterjee, J.-M. Ahn, X. Yang, B. L. Thornton, I. T. Ryde, D. Starnes, and J. N. Meyer, “A micro-sized model for the in vivo study of nanoparticle toxicity: what has Caenorhabditis elegans taught us?,” Environmental Chemistry, vol. 11, no. 3, pp. 227-246, 2014. [268] D. Starnes, J. Unrine, C. Chen, S. Lichtenberg, C. Starnes, C. Svendsen, P. Kille, J. Morgan, Z. E. Baddar, and A. Spear, “Toxicogenomic responses of Caenorhabditis elegans to pristine and transformed zinc oxide nanoparticles,” Environmental pollution, vol. 247, pp. 917-926, 2019. [269] D. K. Sang, H. Wang, Z. Guo, N. Xie, and H. Zhang, “Recent Developments in Stability and Passivation Techniques of Phosphorene toward Next‐Generation Device Applications,” Advanced Functional Materials, vol. 29, no. 45, pp. 1903419, 2019. [270] K. N. Dinh, Y. Zhang, J. Zhu, and W. Sun, “Phosphorene‐based Electrocatalysts,” Chemistry–A European Journal, 2020. [271] Z. Qu, K. Wu, W. Meng, B. Nan, Z. Hu, C.-a. Xu, Z. Tan, Q. Zhang, H. Meng, and J. Shi, “Surface Coordination of Black Phosphorene for Excellent Stability, Flame Retardancy and Thermal Conductivity in Epoxy Resin,” Chemical Engineering Journal, pp. 125416, 2020. [272] H. Li, P. Lian, Q. Lu, J. Chen, R. Hou, and Y. Mei, “Excellent air and water stability of two- dimensional black phosphorene/MXene heterostructure,” Materials Research Express, vol. 6, no. 6, pp. 065504, 2019. [273] S. Bhattacharjee, “DLS and zeta potential–what they are and what they are not?,” Journal of Controlled Release, vol. 235, pp. 337-351, 2016. [274] V. Uskoković, Z. Castiglione, P. Cubas, L. Zhu, W. Li, and S. Habelitz, “Zeta-potential and Particle Size Analysis of Human Amelogenins,” Journal of Dental Research, vol. 89, no. 2, pp. 149-153, 2010. [275] E. W. Nägele, “The transient zeta potential of hydrating cement,” Chemical Engineering Science, vol. 44, no. 8, pp. 1637-1645, 1989/01/01/, 1989. [276] B. Van der Bruggen, J. H. Kim, F. A. DiGiano, J. Geens, and C. Vandecasteele, “Influence of MF pretreatment on NF performance for aqueous solutions containing particles and an organic foulant,” Separation and Purification Technology, vol. 36, no. 3, pp. 203-213, 2004. [277] Y. Yuan, and T. R. Lee, "Contact angle and wetting properties," Surface science techniques, pp. 3-34: Springer, 2013. [278] H. A. Mannan, H. Mukhtar, T. Murugesan, R. Nasir, D. F. Mohshim, and A. Mushtaq, “Recent applications of polymer blends in gas separation membranes,” Chemical Engineering & Technology, vol. 36, no. 11, pp. 1838-1846, 2013. [279] S. P. Nunes, and K. V. Peinemann, “Ultrafiltration membranes from PVDF/PMMA blends,” Journal of Membrane Science, vol. 73, no. 1, pp. 25-35, 1992. [280] X. Dong, H. D. Shannon, A. Amirsoleimani, G. M. Brion, and I. C. Escobar, “Thiol-Affinity Immobilization of Casein-Coated Silver Nanoparticles on Polymeric Membranes for Biofouling Control,” Polymers, vol. 11, no. 12, pp. 2057, 2019. [281] C. Sprick, S. Chede, V. Oyanedel-Craver, and I. C. Escobar, “Bio-inspired immobilization of casein-coated silver nanoparticles on cellulose acetate membranes for biofouling control,” Journal of Environmental Chemical Engineering, vol. 6, no. 2, pp. 2480-2491, 2018.

222

[282] T. S. Chung, S. K. Teoh, and X. Hu, “Formation of ultrathin high-performance polyethersulfone hollow-fiber membranes,” Journal of Membrane Science, vol. 133, no. 2, pp. 161-175, 1997. [283] H.-L. Wu, C.-C. M. Ma, C.-H. Li, T.-M. Lee, C.-Y. Chen, C.-L. Chiang, and C. J. J. o. M. S. Wu, “Sulfonated poly (ether ether ketone)/poly (amide imide) polymer blends for proton conducting membrane,” vol. 280, no. 1-2, pp. 501-508, 2006. [284] H. L. Wu, C. C. M. Ma, C. H. Li, and C. Y. J. J. o. P. S. P. B. P. P. Chen, “Swelling behavior and solubility parameter of sulfonated poly (ether ether ketone),” vol. 44, no. 21, pp. 3128-3134, 2006. [285] G. Rajagopalan, K. Immordino, J. Gillespie Jr, and S. J. P. McKnight, “Diffusion and reaction of epoxy and amine in polysulfone studied using Fourier transform infrared spectroscopy: experimental results,” vol. 41, no. 7, pp. 2591-2602, 2000. [286] T. Dooher, and D. Dixon, “Multiwalled carbon nanotube/polysulfone composites: Using the Hildebrand solubility parameter to predict dispersion,” Polymer Composites, vol. 32, no. 11, pp. 1895-1903, 2011. [287] A. F. J. C. R. Barton, “Solubility parameters,” vol. 75, no. 6, pp. 731-753, 1975. [288] R. Huang, P. Shao, C. Burns, and X. Feng, “Sulfonation of poly (ether ether ketone)(PEEK): kinetic study and characterization,” Journal of applied polymer science, vol. 82, no. 11, pp. 2651-2660, 2001. [289] L. Puro, M. Mänttäri, A. Pihlajamäki, and M. Nyström, “Characterization of modified nanofiltration membranes by octanoic acid permeation and FTIR analysis,” Chemical Engineering Research and Design, vol. 84, no. 2, pp. 87-96, 2006. [290] R. S. Malik, P. Verma, and V. J. E. A. Choudhary, “A study of new anhydrous, conducting membranes based on composites of aprotic ionic liquid and cross-linked SPEEK for fuel cell application,” vol. 152, pp. 352-359, 2015. [291] A. Destainville, E. Champion, D. Bernache-Assollant, and E. Laborde, “Synthesis, characterization and thermal behavior of apatitic tricalcium phosphate,” Materials Chemistry and Physics, vol. 80, no. 1, pp. 269-277, 2003. [292] J. M. Berg, A. Romoser, N. Banerjee, R. Zebda, and C. M. J. N. Sayes, “The relationship between pH and zeta potential of 30 nm metal oxide nanoparticle suspensions relevant to in vitro toxicological evaluations,” vol. 3, no. 4, pp. 276-283, 2009. [293] R. Kumar, S. Seetharamu, and M. J.∼ W. Kamaraj, “Quantitative evaluation of 3D surface roughness parameters during cavitation exposure of 16Cr–5Ni hydro turbine steel,” vol. 320, pp. 16-24, 2014. [294] K. A. Dunphy Guzman, M. P. Finnegan, and J. F. Banfield, “Influence of surface potential on aggregation and transport of titania nanoparticles,” Environmental science & technology, vol. 40, no. 24, pp. 7688-7693, 2006. [295] J. M. Pettibone, D. M. Cwiertny, M. Scherer, and V. H. Grassian, “Adsorption of organic acids on TiO2 nanoparticles: effects of pH, nanoparticle size, and nanoparticle aggregation,” Langmuir, vol. 24, no. 13, pp. 6659-6667, 2008. [296] P. Van de Witte, P. Dijkstra, J. Van den Berg, and J. Feijen, “Phase separation processes in polymer solutions in relation to membrane formation,” Journal of membrane science, vol. 117, no. 1-2, pp. 1-31, 1996. [297] M. Pagliero, A. Bottino, A. Comite, and C. Costa, “Novel hydrophobic PVDF membranes prepared by nonsolvent induced phase separation for membrane distillation,” Journal of Membrane Science, vol. 596, pp. 117575, 2020.

223

[298] D. Kaya, and K. Keçeci, “Track-Etched Nanoporous Polymer Membranes as Sensors: A Review,” Journal of The Electrochemical Society, vol. 167, no. 3, pp. 037543, 2020. [299] L. Yu, M. Kanezashi, H. Nagasawa, and T. Tsuru, “Phase inversion/sintering-induced porous ceramic microsheet membranes for high-quality separation of oily wastewater,” Journal of Membrane Science, vol. 595, pp. 117477, 2020. [300] K. Kimmerle, and H. Strathmann, “Analysis of the structure-determining process of phase inversion membranes,” Desalination, vol. 79, no. 2-3, pp. 283-302, 1990. [301] M. A. Frommer, and D. Lancet, "The mechanism of membrane formation: membrane structures and their relation to preparation conditions," Reverse Osmosis Membrane Research, pp. 85-110: Springer, 1972. [302] Y. Fujii, H. Iwatani, and S. Kigoshi, “Morphological structures of the membranes prepared from polymer solutions,” Polymer journal, vol. 24, no. 8, pp. 737, 1992. [303] B. K. Sah, K. Das, and S. Kundu, “pH-dependent structure, pattern and hysteresis behaviour of lipid (DMPA)-protein (BSA) monolayer complex,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 579, pp. 123663, 2019. [304] K. Cho, J. Yang, and Y. Lu, “Phosphorene: An emerging 2D material,” Journal of Materials Research, vol. 32, no. 15, pp. 2839-2847, 2017. [305] J. Eke, P. A. Mills, J. R. Page, G. P. Wright, O. V. Tsyusko, and I. C. Escobar, “Nanohybrid Membrane Synthesis with Phosphorene Nanoparticles: A Study of the Addition, Stability and Toxicity,” Polymers, vol. 12, no. 7, Jul, 2020. [306] M. Clara, O. Gans, S. Weiss, D. Sanz-Escribano, S. Scharf, and C. J. W. R. Scheffknecht, “Perfluorinated alkylated substances in the aquatic environment: an Austrian case study,” vol. 43, no. 18, pp. 4760-4768, 2009. [307] C. Lau, J. L. Butenhoff, J. M. J. T. Rogers, and a. pharmacology, “The developmental toxicity of perfluoroalkyl acids and their derivatives,” vol. 198, no. 2, pp. 231-241, 2004. [308] B. J. Apelberg, F. R. Witter, J. B. Herbstman, A. M. Calafat, R. U. Halden, L. L. Needham, and L. R. Goldman, “Cord serum concentrations of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) in relation to weight and size at birth,” Environ Health Perspect, vol. 115, no. 11, pp. 1670-6, Nov, 2007. [309] K. M. Rappazzo, E. Coffman, and E. P. Hines, “Exposure to Perfluorinated Alkyl Substances and Health Outcomes in Children: A Systematic Review of the Epidemiologic Literature,” Int J Environ Res Public Health, vol. 14, no. 7, Jun 27, 2017. [310] M. Sáez, P. de Voogt, and J. R. Parsons, “Persistence of perfluoroalkylated substances in closed bottle tests with municipal sewage sludge,” Environmental Science and Pollution Research, vol. 15, no. 6, pp. 472-477, 2008/09/01, 2008. [311] K. Kannan, “Perfluoroalkyl and polyfluoroalkyl substances: current and future perspectives,” Environmental Chemistry, vol. 8, no. 4, pp. 333-338, 2011. [312] K. Kannan, J. Koistinen, K. Beckmen, T. Evans, J. F. Gorzelany, K. J. Hansen, P. D. Jones, E. Helle, M. Nyman, J. P. J. E. s. Giesy, and technology, “Accumulation of perfluorooctane sulfonate in marine mammals,” vol. 35, no. 8, pp. 1593-1598, 2001. [313] L. Ahrens, M. J. E. t. Bundschuh, and chemistry, “Fate and effects of poly‐and perfluoroalkyl substances in the aquatic environment: A review,” vol. 33, no. 9, pp. 1921-1929, 2014. [314] F. Pontius, “Regulation of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonic Acid (PFOS) in Drinking Water: A Comprehensive Review,” Water, vol. 11, no. 10, pp. 2003, 2019.

224

[315] A. Cordner, V. Y. De La Rosa, L. A. Schaider, R. A. Rudel, L. Richter, and P. Brown, “Guideline levels for PFOA and PFOS in drinking water: the role of scientific uncertainty, risk assessment decisions, and social factors,” Journal of Exposure Science & Environmental Epidemiology, vol. 29, no. 2, pp. 157-171, 2019/03/01, 2019. [316] J. Cui, P. Gao, Y. J. E. S. Deng, and Technology, “Destruction of per-and polyfluoroalkyl substances (PFAS) with advanced reduction processes (ARPs): A critical review,” vol. 54, no. 7, pp. 3752-3766, 2020. [317] C. A. Hone, and C. O. Kappe, "The use of molecular oxygen for liquid phase aerobic oxidations in continuous flow," Accounts on Sustainable Flow Chemistry, pp. 67-110: Springer, 2020. [318] A. Gavriilidis, A. Constantinou, K. Hellgardt, K. K. M. Hii, G. J. Hutchings, G. L. Brett, S. Kuhn, and S. P. Marsden, “Aerobic oxidations in flow: opportunities for the fine chemicals and pharmaceuticals industries,” Reaction chemistry & engineering, vol. 1, no. 6, pp. 595-612, 2016. [319] X. Ye, M. D. Johnson, T. Diao, M. H. Yates, and S. S. Stahl, “Development of safe and scalable continuous-flow methods for palladium-catalyzed aerobic oxidation reactions,” Green chemistry, vol. 12, no. 7, pp. 1180-1186, 2010. [320] A. Saad, R. Mills, H. Y. Wan, M. A. Mottaleb, L. Ormsbee, and D. Bhattacharyya, “Thermo-responsive adsorption-desorption of perfluoroorganics from water using PNIPAm hydrogels and pore functionalized membranes,” Journal of Membrane Science, vol. 599, Apr, 2020. [321] M. F. Ismail, B. Khorshidi, and M. Sadrzadeh, “New insights into the impact of nanoscale surface heterogeneity on the wettability of polymeric membranes,” Journal of Membrane Science, vol. 590, pp. 117270, 2019/11/15/, 2019. [322] V. Vatanpour, S. S. Madaeni, R. Moradian, S. Zinadini, and B. Astinchap, “Fabrication and characterization of novel antifouling nanofiltration membrane prepared from oxidized multiwalled carbon nanotube/polyethersulfone nanocomposite,” Journal of membrane science, vol. 375, no. 1-2, pp. 284-294, 2011. [323] X. Zhao, Y. Su, W. Chen, J. Peng, and Z. Jiang, “Grafting perfluoroalkyl groups onto polyacrylonitrile membrane surface for improved fouling release property,” Journal of Membrane Science, vol. 415-416, pp. 824-834, 2012/10/01/, 2012. [324] M. A. Mottaleb, M. C. Petriello, and A. J. Morris, “High-Throughput UHPLC-MS/MS Measurement of Per-and Poly-Fluorinated Alkyl Substances in Human Serum,” Journal of Analytical Toxicology, vol. 44, no. 4, pp. 339-347, 2020. [325] A. Saad, R. Mills, H. Wan, M. A. Mottaleb, L. Ormsbee, and D. Bhattacharyya, “Thermo- responsive adsorption-desorption of perfluoroorganics from water using PNIPAm hydrogels and pore functionalized membranes,” Journal of Membrane Science, vol. 599, pp. 117821, 2020. [326] S. Chede, P. Griffiths, I. C. Escobar, and T. A. L. Harris, “Does casting method matter in filtration membranes? A comparison in performance between doctor blade and slot-die extruded polymeric membranes,” Journal of Applied Polymer Science, pp. 45563-n/a. [327] J. Thompson, G. Eaglesham, J. Reungoat, Y. Poussade, M. Bartkow, M. Lawrence, and J. F. Mueller, “Removal of PFOS, PFOA and other perfluoroalkyl acids at water reclamation plants in South East Queensland Australia,” Chemosphere, vol. 82, no. 1, pp. 9-17, 2011. [328] A. Dreyer, T. Kirchgeorg, I. Weinberg, and V. Matthias, “Particle-size distribution of airborne poly- and perfluorinated alkyl substances,” Chemosphere, vol. 129, pp. 142-9, Jun, 2015.

225

[329] F. Dixit, B. Barbeau, S. G. Mostafavi, and M. Mohseni, “PFOA and PFOS removal by ion exchange for water reuse and drinking applications: role of organic matter characteristics,” Environmental Science: Water Research & Technology, vol. 5, no. 10, pp. 1782-1795, 2019. [330] C. Bellona, and J. E. Drewes, “The role of membrane surface charge and solute physicochemical properties in the rejection of organic acids by NF membranes,” Journal of Membrane Science, vol. 249, no. 1-2, pp. 227-234, 2005. [331] S. Fujii, C. Polprasert, S. Tanaka, N. P. Hong Lien, and Y. Qiu, “New POPs in the water environment: distribution, bioaccumulation and treatment of perfluorinated compounds–a review paper,” Journal of Water Supply: Research and Technology— AQUA, vol. 56, no. 5, pp. 313-326, 2007. [332] Z. Ma, G. Shu, and X. Lu, “Preparation of an antifouling and easy cleaning membrane based on amphiphobic fluorine island structure and chemical cleaning responsiveness,” Journal of Membrane Science, vol. 611, pp. 118403, 2020/10/01/, 2020. [333] R. Giri, H. Ozaki, T. Morigaki, S. Taniguchi, and R. Takanami, “UV photolysis of perfluorooctanoic acid (PFOA) in dilute aqueous solutionR. R. Giri et al. UV photolysis of perfluorooctanoic acid (PFOA) in dilute aqueous solution,” Water Science and Technology, vol. 63, no. 2, pp. 276-282, 2011. [334] Q. Li, and M. Elimelech, “Synergistic effects in combined fouling of a loose nanofiltration membrane by colloidal materials and natural organic matter,” Journal of Membrane Science, vol. 278, no. 1, pp. 72-82, 2006/07/05/, 2006. [335] W. Song, V. Ravindran, B. E. Koel, and M. Pirbazari, “Nanofiltration of natural organic matter with H2O2/UV pretreatment: fouling mitigation and membrane surface characterization,” Journal of Membrane Science, vol. 241, no. 1, pp. 143-160, 2004. [336] B. Gomez-Ruiz, P. Ribao, N. Diban, M. J. Rivero, I. Ortiz, and A. Urtiaga, “Photocatalytic degradation and mineralization of perfluorooctanoic acid (PFOA) using a composite TiO2− rGO catalyst,” Journal of hazardous materials, vol. 344, pp. 950-957, 2018. [337] H. Javed, C. Lyu, R. Sun, D. Zhang, and P. J. Alvarez, “Discerning the inefficacy of hydroxyl radicals during perfluorooctanoic acid degradation,” Chemosphere, vol. 247, pp. 125883, 2020. [338] H. Hori, A. Yamamoto, E. Hayakawa, S. Taniyasu, N. Yamashita, S. Kutsuna, H. Kiatagawa, and R. Arakawa, “Efficient decomposition of environmentally persistent perfluorocarboxylic acids by use of persulfate as a photochemical oxidant,” Environmental Science & Technology, vol. 39, no. 7, pp. 2383-2388, 2005. [339] J. Huang, X. Wang, Z. Pan, X. Li, Y. Ling, and L. Li, “Efficient degradation of perfluorooctanoic acid (PFOA) by photocatalytic ozonation,” Chemical Engineering Journal, vol. 296, pp. 329-334, 2016/07/15/, 2016. [340] Y. Wang, P. Zhang, G. Pan, and H. Chen, “Ferric ion mediated photochemical decomposition of perfluorooctanoic acid (PFOA) by 254nm UV light,” Journal of Hazardous Materials, vol. 160, no. 1, pp. 181-186, 2008/12/15/, 2008. [341] W. Zhu, M. N. Yogeesh, and D. Akinwande, "Flexible Phosphorene Devices and Circuits," Micro- and Nanotechnology Sensors, Systems, and Applications Vii, Proceedings of SPIE T. George, A. K. Dutta and M. S. Islam, eds., 2015. [342] S. Mikhailenko, S. Zaidi, and S. Kaliaguine, “Electrical properties of sulfonated polyether ether ketone/polyetherimide blend membranes doped with inorganic acids,” Journal of Polymer Science Part B: Polymer Physics, vol. 38, no. 10, pp. 1386-1395, 2000.

226

[343] C.-F. o. de Lannoy, D. Jassby, K. Gloe, A. D. Gordon, and M. R. Wiesner, “Aquatic biofouling prevention by electrically charged nanocomposite polymer thin film membranes,” Environmental science & technology, vol. 47, no. 6, pp. 2760-2768, 2013.

227

VITA Joyner Eke Education Doctor of Philosophy, Chemical Engineering August 2015 – pending for December 2020 University of Kentucky, Lexington, Kentucky, USA Bachelor of Science, Chemical Engineering November 2006 – March 2012 Obafemi Awolowo University, Nigeria Professional Positions Sandrell Investments July 2013 – August 2014 Process Engineer Lagos, Nigeria Exxon Mobil Producing September 2010 – February 2020 Process Engineering Intern AkwaIbom, Nigeria AWARDS University of Kentucky, College of Engineering Whalen Fellowship, 2019 Mark of Distinction, National Science Foundation EPSCoR, 2017, 2019 Best presentation, 2019, North American Membrane Society, Pittsburgh, PA Most outstanding student research, 2018 Kentucky Water Research Institute, Lexington, KY Student poster awards, 2016, North American Membrane Society, Bellevue, WA North American Membrane Society Elias Klein Award, 2015 University of Kentucky, CME Tuition and Stipend Scholarship, 2015-2020 Julius Madu Scholarship for Umukpehi Women in Engineering Award, 2008 – 2011 JOURNAL PUBLICATIONS Eke, J.; Yusuf, A.; Sodiq, A.; Giwa, A., The global status of desalination: an assessment of current desalination technologies, plants, and capacity. Desalination,495, 114633 Eke, J., Mills, P. A., Page, J. R., Wright, G. P., Tsyusko, O. V., & Escobar, I. C. (2020). Nanohybrid Membrane Synthesis with Phosphorene Nanoparticles: A Study of the Addition, Stability and Toxicity. Polymers, 12(7), 1555. Yusuf, Ahmed, Ahmed Sodiq, Adewale Giwa, Joyner Eke, Oluwadamilola Pikuda, Giorgio De Luca, Javier Luque Di Salvo, and Sudip Chakraborty. "A Review of Emerging

228

Trends in Membrane Science and Technology for Sustainable Water Treatment." Journal of Cleaner Production (2020): 121867 Esfahani, M. R.; Aktij, S. A.; Dabaghian, Z.; Firouzjaei, M. D.; Rahimpour, A.; Eke, J.; Escobar, I. C.; Abolhassani, M.; Greenlee, L. F.; Esfahani, A. R., Nanocomposite Membranes for Water Separation and Purification: Fabrication, Modification, and Applications. Separation and Purification Technology 2019, 213 ,465- 499 Eke, J.; Elder, K.; Escobar, I., Self-Cleaning Nanocomposite Membranes with Phosphorene-Based Pore Fillers for Water Treatment. Membranes 2018, 8 (3), 79 Eke, J.; Wagh, P.; Escobar, I. C., Ozonation, Biofiltration and the Role of Membrane Surface Charge and Hydrophobicity in Removal and Destruction of Algal Toxins at basic pH values. Separation and Purification Technology 2018, 194, 56-63

229