Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Karen Giovanna Bastidas Gómez
Universidad Nacional de Colombia Facultad de Ingeniería Departamento de Ingeniería Química y Ambiental Bogotá, Colombia 2016
Tratamiento de aguas residuales usando un nanocatalizador soportado en fibras de Fique y fase activa de hierro
Karen Giovanna Bastidas Gómez
Universidad Nacional de Colombia Facultad de Ingeniería Departamento de Ingeniería Química y Ambiental Bogotá, Colombia 2016
Tratamiento de aguas residuales usando un nanocatalizador soportado en fibras de Fique y fase activa de hierro
Karen Giovanna Bastidas Gómez
Tesis presentada como requisito parcial para optar al título de Magister en Ingeniería – Ingeniería Química
Director: Hugo Ricardo Zea Ramírez, Ph.D.
Codirector: Cesar Augusto Sierra Ávila, Ph.D.
Línea de investigación: Materiales y tratamiento de residuos acuosos Grupo de Investigación: Materiales, Catálisis y Medio Ambiente
Universidad Nacional de Colombia Facultad de Ingeniería Departamento de Ingeniería Química y Ambiental Bogotá, Colombia 2016
“Research is to see what everybody has seen and think what nobody has thought”
Albert Szent-Györgyi
Acknowledgements
Without God, it would not have been possible to carry out what it may be one of the best times of my life. Thank you for providing so much joy, patience, courage and conviction to do what I like so much, for never letting me fall and always shedding light on the path I have to take.
I would also like to thank the best medicine anyone can have: Fannytidina, you are and you will always be my example to follow, you're the superheroine who taught me to be the woman that I am, thank you for teaching me to never give up and have faith despite adversity. When I was cold and hungry doing experiments, you always had a big smile and a hug for me, I love you with all the strength in my heart. Fo, thanks for the many dawns when our songs and desire to succeed motivated us to work in that makes us happy, for helping me to dream and believe about what is invisible to our soul. To my family, who always reminded me our love for each other is the biggest treasure we have, no matter where we are, our hearts are always together full with best wishes.
Thanks to my advisor Professor Hugo Ricardo Zea Ramírez, for the countless lessons I learnt from you, not only from the great academic training that I received, but also because I have learnt the value of living with tranquility and peace, thank you for all the support, for believing in me when I arrived to that unknown world called Universidad Nacional de Colombia. I can now say that it possible for everyone to fly from the creativity and freedom of doing science through the mind and heart with the research group of Materials, Catalysis and Environment.
Likewise, I’m grateful to Professor Cesar Augusto Sierra Avila and the Macromolecules research group, for taking me in with arms wide open, thank you for that little family we have, for the Friday Group cultural meeting and all those moments we shared, regardless of occupations and distance.
Day by day I met people who made more enjoyable my path and who helped me accomplish this research, you gave me more than just pieces of knowledge, you gave me a part of your heart: Cristo, Tati, Andre, Snorkey, Alejo, Figaro, Pocho, Ruby, Eevee, Fran, Peter, Geral, Carito, Darks and Loretto, thank you for the unconditional support, for the countless laughter that we shared and brought so much joy to my spirit. Especially Chucks, thank you for giving so much color the days that seemed gray and unlit, for loving me in this supernatural way you only do; thanks for always having the perfect words and know how to fix everything, thanks for giving me the chance to get to know you. You'll always have a place in my heart.
Thanks to Anita and Davidcito “my children”, to make the best working group. You were always ready to learn, thanks for all your energy and willingness to help in some way to achieve our goals, for allowing me to dream with you and show you that flying high is only a matter of desire, that if we work together with a clear goal, we will always shine. Thanks for these times in which the laughter were our engine to keep moving.
I thank all the faculty members, administration and laboratory staff of the Chemical and Environmental Engineering Department, who stretched their hands and contributed to my personal and professional training. Thanks to the Research Division in Bogota (DIB) for providing financial resources through the project "Tratamiento de aguas residuales usando un nanocatalizador soportado en fibras de fique y fase activa de hierro." Finally, thanks to the Universidad Nacional de Colombia, for giving me the opportunity to learn a way to interpret reality from the concept of science, to provide solutions to different problems for our country and for the world.
Resumen
El tratamiento de aguas residuales industriales para la decoloración y la remoción de metales pesados utilizando procesos heterogéneos, económicos y factibles ha sido un tema de interés a escala industrial. Actualmente ciencias como la nanotecnología han potencializado las propiedades de materiales compuestos, los cuales han permitido incursionar en el uso de nanopartículas, como fase activa para catalizadores. Particularmente, las nanopartículas de hierro se han utilizado en la remoción de metales pesados como el mercurio y el arsénico a través de operaciones como la adsorción y han sido utilizadas en procesos avanzados de oxidación en los cuales, a partir del proceso Fenton, se realiza la degradación y mineralización de aguas provenientes de industrias textiles. Adicionalmente, la necesidad actual de generar productos y procesos de carácter sostenible ha hecho posible la implementación del uso de fibras naturales como matrices potenciales de materiales compuestos. Es por esta razón que hoy en día mucha de la investigación se ha focalizado en el uso de materiales lignocelulósicos, con el fin de aprovechar las propiedades mecánicas, físicas y químicas que posee la celulosa. En esta tesis de maestría, se obtuvo un material catalítico a partir del uso de la fibra de fique como soporte de nanopartículas de hierro. Con el objetivo de hacer posible el proceso del anclaje de nanopartículas, se realizó una preparación de la fibra la cual consistió en una funcionalización del soporte para posteriormente depositar las nanopartículas de hierro por medio de un método fácil y económico de síntesis de nanopartículas como lo es la impregnación húmeda; así mismo, para conocer las propiedades relativas al material se realizó una caracterización fisicoquímica por medio de métodos analíticos gravimétricos, volumétricos e instrumentales. Esta tesis de maestría también exploró potenciales aplicaciones en el tratamiento de aguas residuales, dentro de las cuales se encontraron resultados prometedores en relación a la degradación y mineralización de colorantes tipo azo como el Orange II y en la remoción de metales pesados como el mercurio. Ambas aplicaciones fueron analizadas con el fin de comprender las variables fundamentales de los procesos de adsorción y reacción involucrados.
Palabras clave: Furcraea andina, nanopartículas de hierro, mercurio, Orange II, tratamiento aguas residuales.
Abstract
Treatment of industrial wastewater for bleaching and removal of heavy metals using heterogeneous, economic and feasible processes has been a topic of interest at industrial scale. Currently, sciences such as nanotechnology have potentiated the properties of composite materials, which have enabled the use and implementation of nanoparticles as active phase in catalysts and adsorbent materials. Particularly, iron nanoparticles have been used in the removal of heavy metals such as mercury and arsenic through operations such as adsorption and they have been used in advanced oxidation processes in which, Fenton process of degradation and mineralization of water from textile industries is performed. In addition, the current need to generate products and processes with sustainable basis has made possible the implementation of the use of natural fibers as potential matrices of composite materials. For this reason today much of the research has focused on the use of lignocellulosic materials, in order to exploit the mechanical, physical and chemical properties of cellulose. In this MSc thesis, a catalytic material was developed from the use of fique fiber as support of iron nanoparticles. A pretreatment of the raw fiber was performed in order to create the appropriate chemical an physical conditions on the fiber surface to support the iron; a functionalization process was carried out to further improve the anchorage to the surface; finally, wet impregnation was used to incorporated iron nanoparticles on the support surface. A detailed characterization of the synthesized material was performed via by gravimetric, volumetric and instrumental analytical methods. This MSc thesis also explore potential applications in the treatment of wastewater, in which promising results were found with respect to degradation and mineralization of azodyes such as Orange II and the removal of heavy metals such as mercury. Both applications were analyzed in order to understand the relevant variables involved during the adsorption and reaction processes.
Keywords: Furcraea andina, iron nanoparticles, mercury, Orange II, wastewater treatment.
Preface
The research developed in the MSc thesis is the continuation of a work that Chacón, Combariza and Hinestroza [1], in the year 2013 began at the Universidad Industrial de Santander (UIS). They performed a material for degradation of the dye indigo carmine using a biocomposite of nanostructured from MnO2 and fique fibers. It was interesting for me, because since my undergraduate thesis I found possible applications that might add value to a residue as the fique fiber, accepting challenges from the social point of view (waste water treatment to increase access to the natural resource and time to help the fiquer community increasing their motivation in the crop), economic (synthesis of an economic and feasible catalyst from composite materials that the process of scaling to render practicable), environmental (contribution to issues such as the use of waste and decontamination of liquid effluent) and technical (implementation combined with the use of natural fibers and nanotechnology).
The general objective of this thesis is to develop an active, stable and inexpensive catalytic material, using iron nanoparticles, supported in fique fiber for water treatment processes of aqueous liquid effluents contaminated with metals and organic compounds and the specific objectives are: 1) Synthesizing an iron nanoparticles catalyst supported on fique fiber, 2) to characterize structural, thermal and mechanically the catalyst obtained, and 3) to evaluate the ability of the catalyst on the removal of mercury ions and dye Orange II. The first and second specific objectives were accomplished in the work presented in Chapters 2 and 3, while the third specific objective was achieved in Chapters 4 and 5. One of the underlying goals of this thesis is to provide the research group and anyone who want to research on this field with the basic knowledge about the main concepts. This is why the Chapter 1 of this thesis is a general introduction to the topics developed in this thesis.
The final point to address in this preface is the language of this document and the structure of the chapters. All chapters, except for the introduction, were written as individual papers with the aim to be submitted to international journals for publication.
Contents
Page
Acknowledgements ...... XIX Resumen...... XXI Abstract ...... XXIII Preface...... XXVI List of Figures ...... 21 List of Tables ...... 25 Chapter 1. Introduction ...... 27 Decontamination treatments of water-dye systems ...... 35 Catalysts supports ...... 37 Iron nanoparticles ...... 44 References ...... 47 Chapter 2. Physochemical treatment and characterization of Furcraea andina ...... 54 Abstract: ...... 54 Keywords: ...... 55 Introduction ...... 55 Materials and methods ...... 56 Materials ...... 56 Fiber pretreatment ...... 56 Fiber functionalization ...... 56 Characterization ...... 57 Humidity ...... 57 Chemical structural components ...... 57 Surface characterization ...... 58 Structural characterization ...... 59 Morphological and textural characterization ...... 59 Thermal characterization...... 60 Results and discussion ...... 60 Fiber pretreatment ...... 60 Fiber functionalization ...... 63 Surface characterization ...... 63
Contents XVIII
Structural characterization ...... 67 Morphological and textural characterization ...... 70 Thermal characterization...... 73 Conclusions...... 74 References ...... 75 Chapter 3. Impregnation of iron compounds on natural and modified fique fiber ...... 79 Abstract: ...... 79 Keywords: ...... 79 Introduction ...... 80 Materials and methods: ...... 81 Catalyst Preparation ...... 81 Characterization ...... 83 Results and discussion ...... 84 Impregnation process ...... 84 Mechanical characterization ...... 95 Conclusions...... 98 References ...... 100 Chapter 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalysts ...... 104 Abstract: ...... 104 Keywords: ...... 104 Introduction ...... 104 Materials and methods ...... 107 OII degradation ...... 107 Effect of chloride ion ...... 109 Total Organic Carbon (TOC) and Total Nitrogen (TN) analysis ...... 109 Identification of intermediate products resulting from the treatment of OII ...... 110 Results and discussion ...... 110 OII degradation ...... 110 Effect of chloride ion ...... 122 Total Organic Carbon (TOC) and Total Nitrogen (TN) analysis ...... 123 Conclusions...... 126 References: ...... 127 Chapter 5. Studies on adsorption mercury from aqueous solution on biocomposite material from fique fiber and iron nanoparticles ...... 131 Abstract: ...... 131 Contents XIX
Keywords: ...... 131 Introduction ...... 131 Materials and methods ...... 133 Conclusions...... 145 References ...... 146 Conclusions and recommendations ...... 150 Annex ...... 153 Annex 1 ...... 153 Annex 2 ...... 160 Annex 3 ...... 163 Annex 4 ...... 164 Annex 5 ...... 166 Annex 6 ...... 167 Annex 7 ...... 168
List of Figures
Figure 1.1. Structural formula of the azo dye Orange II [ ...... 28 Figure 1.2. Details of the cellulosic fiber structure 2 ...... 38 Figure 1.3. Molecular structure of hemicellulose 3 ...... 38 Figure 1.4. Molecular structure of Lignin4 ...... 38 Figure 1.5. Furcraea andina (Personal archive) 5 ...... 40 Figure 1.6. Potential uses of the products resulting from fique 6 ...... 41 Figure 2.1. Route used for functionalization of pretreated fique fiber 7 ...... 57 Figure 2.2. pHzpc for the fiber according to treatment 8 ...... 64 Figure 2.3. FTIR - ATR spectrum of raw fique fiber, pretreated and functionalized ...... 65 Figure 2.4. EDS profile of raw, pretreated and functionalized fique fibers 10 ...... 67 Figure 2.5. XRD of raw and pretreated fiber (30, 60 and 90 minutes of sonication) 11 ..... 67 Figure 2.6. XRD of raw and functionalized fiber (1, 2 and 3 hrs of functionalization) 12 ... 68 Figure 2.7. SEM micrographs of the raw fiber 13 ...... 71 Figure 2.8. SEM of the pretreated fiber M60 14...... 72 Figure 2.9. SEM of functionalized fiber MC3 15 ...... 72 Figure 2.10. TGA for raw, pretreated and functionalized fiber 16 ...... 74 Figure 3.1. Mechanism of formation of iron nanoparticles 17 ...... 82 Figure 3.2. Color change on impregnated fibers 18 ...... 84 Figure 3.3. Amount of Fe species impregnated on raw, pretreated and functionalized fiber as a function of impregnation days 19 ...... 85 Figure 3.4. Chemical synthesis of nanoparticles by the impregnation method 20 ...... 86 Figure 3.5. XRD diffractogram profiles of functionalized fiber after 1, 2 and 3 days of impregnation.21 ...... 89 Figure 3.6. FTIR spectrum of functionalized fiber after three different days of impregnation (1, 2 and 3 days) and without impregnation 22 ...... 91 Figure 3.7. Morphological analysis of the functionalized fiber surface after 1 day of impregnation 23 ...... 93 Figure 3.8. SEM pictures of the functionalized fiber surface after 2 days of impregnation 25 ...... 94 Figure 3.9. Size distribution leached of iron nanoparticles (1day of impregnation) in aqueous solution (Malvern Zetasizer Software)26 ...... 95 Contents XXII
Figure 3.10. Curves stress vs strain of a) raw fiber b) catalyst with 1 day of impregnation c) catalyst with 2 day of impregnation d) catalyst with 3 day of impregnation 27 ...... 97 Figure 4.1. OII degradation after 4 hours of catalytic activity performed under the following conditions: Experiment 1 (Catalyst Fe10.9 wt.% and Dye 퐶푂퐼퐼0: 2푥10 − 4푀), Experiment 2 (Dye 퐶푂퐼퐼0: 2푥10 − 4푀 and oxidizing agent 퐶퐻2푂20: 5.05푥10 − 3푀), Experiment 3 (Catalyst 10.9 Fe wt.%, Dye 퐶푂퐼퐼0: 2푥10 − 4푀, catalyst contained in aromatic bag28 ... 111 Figure 4.2. OII degradation after 4 hours of catalytic activity performed under the following conditions: pH: 2.5, 퐶푂퐼퐼0: 1.1푥10 − 4푀, 퐶퐻2푂20: 5.05푥10 − 3푀 and 10.9푤푡. % 29 ...... 111 Figure 4.3. Experimental and calculated results of the experimental design for Orange II oxidation. Degradation Response (%)30 ...... 114
Figure 4.4. Residual plots for kapmod 31 ...... 114
Figure 4.5. Contour plot of Degradation (%) vs H2O2 and pH 32 ...... 116 Figure 4.6. Contour plot of Degradation (%) vs %Fe and pH 33 ...... 117
Figure 4.7. Contour plot of Degradation (%) vs COIIo and pH 34 ...... 117 Figure 4.8. Degradation OII, the left part initial color and the right the color after the treatment under the conditions: pH: 2.5, COII0: 1.1x10 − 4M, CH2O20: 5.05x10 − 3M and 10.9 Fe wt. %)35 ...... 118 Figure 4.9. Effect of temperature ions in OII degradation after 4 hours of catalytic activity under these conditions: pH: 2.5, 퐶푂퐼퐼0: 1.1푥10 − 4푀, 퐶퐻2푂20: 5.05푥10 − 3푀 and 10.9 퐹푒 %푤푡 36 ...... 120 Figure 4.10. Cycle number of use of OII degradation after 4 hours of catalytic activity under these conditions: pH: 2.5, 퐶푂퐼퐼0: 1.1푥10 − 4푀, 퐶퐻2푂20: 5.05푥10 − 3푀 and 10.9 퐹푒 푤푡. % 37 ...... 121 Figure 4.11. XRD of catalyst before and after Orange II treatment38 ...... 122 Figure 4.12. Effect of chloride ions in OII degradation after 4 hours of catalytic activity under these conditions: pH: 2.5, 퐶푂퐼퐼0: 1.1푥10 − 4푀, 퐶퐻2푂20: 5.05푥10 − 3푀 and 10.9 퐹푒 푤푡%39 ...... 123 Figure 4.13. Structural formula of the azo dye Orange II 40 ...... 124 Figure 4.14. Chromatogram obtained with a UV-Vis detector at 483 nm of OII dye before and after degradation 41 ...... 125 Figure 4.15. Chromatogram obtained with a UV-Vis detector at 230 nm related with benzene 42 ...... 125 Figure 4.16. Chromatogram obtained with a UV-Vis detector at 310 nm related with naphthalene 43 ...... 126 Contents XXIII
Figure 5.1. Percentage of removal at different loads of adsorbent material (pH=10, initial concentration of mercury = 10ppm and 10.9 wt.% Fe)44 ...... 135 Figure 5.2. Final removal percentage of removal at different loads of adsorbent material (pH=10, initial concentration of mercury = 10 ppm and 10.9 wt.% Fe) 45 ...... 136 Figure 5.3. Mercury removal using raw fique fiber (pH=10, initial concentration of mercury =10ppm).46 ...... 137 Figure 5.4. Experimental and calculated results of the experimental design for mercury removal. Responses considered removal % 47 ...... 142
Figure 5.5. Residual plots for qe 48 ...... 143
Figure 5.6. Contour plot of qe (mg/g) vs. pH and mercury initial concentration 49...... 144
Figure 5.7. Contour plot of qe (mg/g) vs. Fe wt% and mercury initial concentration 50 ... 145
List of Tables
Table 1.1. Degradation treatment of Orange II (OII) ...... 28 Table 1.2. Influence factors on the adsorption ...... 31 Table 1.3. Most common adsorbent materials ...... 32 Table 1.4. Mechanisms used in mercury removal 4 ...... 34 Table 1.5. Removal of mercury with residual biomass 5...... 34 Table 1.6. Conventional treatment for water decontamination 6 ...... 36 Table 1.7. Methods of cellulose fibers preparation 7 ...... 39 Table 1.8. Average weight distribution of the fique leave components, usable percentage and applications 8 ...... 40 Table 1.9. Main components of fique fiber 9 ...... 41 Table 1.10.10Fique fiber quality standards classification ...... 42 Table 2.1. Fique fiber proximate analysis and structural carbohydrates and lignin (NREL) analyses 11 ...... 61 Table 2.2. Lignin content in fique fiber pretreated at different times 12 ...... 61 Table 2.3. Carbohydrates present in raw and pretreated fique fiber 13 ...... 63 Table 2.4. Results of the acidic and basic sites in the fique fiber in different stages of analysis 14 ...... 65 Table 2.5. Crystallinity index for raw, pretreated and functionalized fique fiber 15 ...... 68 Table 2.6. Calculated average crystallite size for raw, pretreated and functionalized fique fiber 16 ...... 70 Table 2.7. BET surface area of raw, pretreated and functionalized fibers17...... 73 Table 3.1. XRF analysis of raw fique fiber and catalyst with 1 day of impregnation 18 ..... 87 Table 3.2. Acidic and basic sites determined by titration Boehm and pHzpc for the impregnated functionalized fiber 19 ...... 92 Table 3.3. BET surface area of functionalized fiber after impregnation 20 ...... 92 Table 3.4. Summary of mechanical characterization for raw and impregnated fiber (1, 2 and 3 days) 21 ...... 96 Table 4.1. Factors evaluated in the dye degradation of OII using iron supported on fique catalyst 22 ...... 108 Table 4.2. Experiments values of Box - Behnken experimental design, degradation percentage obtained for each experimental conditions 23 ...... 112 Contents XXVI
Table 4.3. Analysis of variance (ANOVA) for percentage of degradation by MiniTab 16 Statistical Software24 ...... 113 Table 4.4. Simplified pseudo-first-order kinetic analysis 25 ...... 120 Table 4.5. Total Organic Carbon (TOC) and Total Nitrogen (TN) analysis results 26 ..... 124 Table 5.1. Factors assessed in mercury removal using a adsorbent from Fique and iron nanoparticles27 ...... 134 Table 5.2. Adsorption isotherms models 28 ...... 137 Table 5.3. Langmuir and Freundlich isotherm models results for the Hg adsorption on raw fique fiber 29 ...... 138 Table 5.4. Experimental levels used in the design of experiments Box - Behnken and values obtained for the Langmuir isotherm model and Langergren model of adsorption 30 ...... 138 Table 5.5. Pseudo-second-order kinetic model of adsorption 31 ...... 139 Table 5.6. Experimental levels used in the design of experiments Box - Behnken and values obtained for the Lagergren Pseudo-second-order kinetic model 32...... 139
Table 5.7. Analysis of variance (ANOVA) for qe (mg/g) by MiniTab 16 Statistical Software 33 ...... 141
1. Introduction 27
Chapter 1. Introduction
The spread of a wide range of contaminants in surface and groundwater has become a critical issue worldwide, due to population growth, rapid industrialization and development of long-term drought. Persistent pollutants in wastewater include heavy metals, inorganic and organic molecules, and many other complex compounds. As a result, the number of available water resources in nature to sustain life has been decreasing over time, becoming one of the biggest problems nowadays, because of the diversity of pollutants and the rapid depletion of available sources. Therefore, there is the need for controlling the harmful effects of pollutants and to improve the conditions of human life.
Industrial processes related to food and textiles, among others, use natural or artificial dyes, which are irresponsible and constantly discharges into rivers and seas. In particular, in Colombian, due to the presence of an active textile industry in the vicinity of the Medellín river, regional and national authorities have shown a growing interest into have some cost effective solutions.
The dyes and pigments industry plays an important role in several economic sectors, for example textile and food. There are important differences between pigments and dyes; a pigment is a colored, insoluble substance that does not adhere directly to the substrate, but through an adherent vehicle, usually a polymer, which supports and adheres to the substrate [1]. Dyes are chemical compounds that after applied to a substrate (textile fiber, paper, plastic, leather or foods), they can be absorbed on it, providing a permanent color. Dyes are usually applied in solution or emulsions that presents affinity to the substrate in which is going to be absorb. Current world dyes production is in the order of 90 million kg per year [2].
Dyes can be classified using different characteristics; they can be natural or artificial, also depending on the chemical structure (organic or inorganic) [3]. Another way to classified dyes is based on the method use to apply them: reactive, disperse, direct, sulfur, basic cationic, anionic or acid, mordant, solvent dyes, among others. 28 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
One of the most representative dye in the textile industry and also one that shows increasing challenges for its treatment is Orange II (C16H11N2NaO4S). Orange II is a heterocyclic anionic azo compound from the group of naphthols (Figure 1.1), use as dye in textile, cosmetic, silk and paper industries [9]. Orange II is also known as: OII, acid orange 7, acid orange A, 2-naphthol orange, CI 15510, D&C orange 4, COLIPA C015 and sodium 4-[(2E)-2-(2-oxonaphthalen-1-ylidene)hydrazinyl]benzenesulfonate [4].
Figure 1.1. Structural formula of the azo dye Orange II [4]
Orange II is a non-biodegradable azo-dye commonly emitted by the textile industry in waste water effluents [5, 6]. It poses a potential risk to human health and has even been reported as carcinogenic [7, 8]. Some degradation treatment methods developed for Orange II are listed in Table 1.1: Table 1.1. Degradation treatment of Orange II (OII) Heterogeneous It has been investigated the effects of pH, temperature, Cl- ions Fenton-like concentration, O-II initial concentration, hydrogen peroxide and process using a ferrous ion catalyst (Fe2+) concentrations in the degradation rate. zeolite Y-Fe Also, it was validated in a continuous stirred tank reactor (CSTR), achieving O-II final concentrations of 5.9 × 10−5 M [5]. Fenton-like Degradation and mineralization of O-II solutions using impregnated oxidation using saponite with different iron salts (iron(II) ethyl acetate, iron(II) oxalate heterogeneous and iron(II) acetylacetonate and loads of 7.5, 13.0 y 17 % in weight). catalyst based The best conditions achieved degraded 99% of dye with 91% on bentonite reduction of total organic carbon (TOC) at 70°C, using only 90 mg of clay catalyst per liter of solution, and the amount of iron leached in the final solution was less than 1 ppm [6]. Heterogeneous Heterogeneous Fenton-like oxidation process, used hydrogen Fenton-like peroxide for catalyst activation with two types of carbon support oxidation using (active carbon and iron oxide aerogel) impregnated with iron (7% in catalyst of weight). The catalyst based on aerogel showed good catalytic yield, carbon-Fe with mineralization up to 90%. However, iron leaching is considerable, generating a progressive deactivation [7]. However, contamination of water sources is not only due to industrial processes related with textiles and dyes. Also, mining processes generated heavy metals residues and transforms environmental ecosystem conditions (temperature, pH, salinity), thereby 1. Introduction 29 increasing the toxicity of effluents. Particularly, mercury has become an important vector of contamination in areas were mining of noble metals is active (especially in illegal extraction operations). Mercury is a high density heavy metal, silver in appearance, liquid at room temperature, presenting toxic effects on living beings and having the capability to accumulate in food chains [8]. It has physicochemical properties such as high thermal and electrical conductivity, high surface tension and chemical stability, making it a useful material in the production of thermometers and other measuring instruments, dentistry, batteries, electronic, electrical and lighting components [9].
Mercury is found naturally in the planet, due to erosion of earth's crust and volcanic activity [10]. Mercury occurs in deposits throughout the world mostly as cinnabar (mercury sulfide). It is also release as a byproduct in many chemical processes such as coal burning and chlorination plants among others; however, one of the major source of mercury contamination is the gold extraction process [8].
Hg can exist in several forms: elemental (metallic), inorganic or organic (such as methylmercury, which enters the human body through food) [10]. Particularly, methylmercury presents an aggravating problem because is retained in the membranes of autotrophs organism, then, as heterotrophic organisms feed on autotrophs it becomes an accumulated material in the food chain; specifically fishes accumulate Hg in great quantities as methyl mercury, which are subsequently consumed by humans [11].
This metal could be a potentially harmful substance to humans and the extent of its health impact depends on variables as: compound state (organic, elemental, inorganic), degree of exposure, exposure source, route of absorption, concentration and interaction with other substances [9], [12]. Exposure to mercury in the short and long time, may cause serious health problems, such as: brain damage, kidney damage, lung, digestive system problems, tremors, changes in vision and hearing, insomnia, memory disorders, nausea, vomit, diarrhea, seizures, among others [13].
The Environmental Protection Agency (EPA) has developed regulations related to the maximum allowable concentration for methylmercury in water, estuarine fish and shellfish tissue to ensure the safety of the population that consumes or handles this kind of food [8]. The current reference dose (RfD) is 0.1 μg/kg/day [9]. 30 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Additionally, organizations like the FDA (Food and Drugs Administration) established a dose of 0.23μg/kg/day, recommending that pregnant women limit fish consumption, likewise other world organizations (WHO, World Helth Organization and ATSDR, Agency for Toxic Substances and Disease Registry) determine levels up to 0.47 μg/kg/day, respectively [8].
According to the WHO, mercury is one of ten products or groups of chemicals that pose special public health problem due to its high contamination potential and its widespread use in not regulated industries [10]. This last issue is of special interest in Colombia, where illegal mineral extraction use extensive quantities of mercury, affecting both atmospheric and water quality [14]. This problem is particularly alarming in the small-scale gold mining process (usually artisanal performed), where one kilogram of gold obtained released into the environment three to five kilograms of mercury [15]. Increasing the statistics of Colombians health problems related to neurological symptoms, decreased motor skills, impaired hearing and vision, among others [8]. Although gold mining is an activity with significant importance in Colombian economy (producing 30 tons per year), environmental control is poorly structured, especially in the areas where handmade extraction is practiced; creating at the same time environmental liabilities, turning this practice into an unsustainable process [15] [16].
Since 2009, Antioquia have imported 520 tons of mercury, from countries such as Mexico, Germany, Spain, United States and the Netherlands. Affecting the population health of at least 16 municipalities, considering Antioquia the most polluted region in the world with mercury and rivers in the Segovia and Remedios area as the third most contaminated rivers with this metal [17]. Similarly, in Choco, gold mining is promoted through the burning of amalgam, which is the mixture of gold with mercury. In one of the latest reports, there are 80 municipalities in 17 departments of Colombia contaminated with mercury, cyanide and fuels, resulting from informal gold mining [20].
Mercury pollution have caused several impacts in hydric resources such as the reduction of dissolved oxygen in effluents, obstruction of water flow and ecosystem modifications by environmental implications on flora and fauna [16]. There are some studies reporting concentrations of total mercury as high as 6,118 ppm, which are above the established values by national and international standards [18]. 1. Introduction 31
The maximum allowed Hg concentration in Colombia is regulated by the National Legislative Decree 3930 of 2010 [19], in which Article 20 considers mercury as a substance of health interest. Articles 38 and 39, in the same decree, state that the maximum permissible concentration for human and domestic consumption is 0.002 mg/L. The same decree cover the maximum concentration in products of the livestock sector (Article 41, 0.01mg/L). Additionally, Article 91 prohibited the discharge of any mercury contaminated waste into water bodies, such as the ones used to provided potable water to human population [19]. Decree 475 of 1998 defines 0.001 mg/L to be the maximum value of total mercury in water permitted in Colombia; however, none of the decrees set limits for methylmercury.
Mercury separation through “adsorption” specifically by physisorption, leverage the physical interactions between the solid surface and the adsorbate. The adsorptive separation is based on three different mechanisms: steric (the adsorbent has pores of such size that allows to pass only molecules with a specific size), kinetic (different diffusion rates of compounds in the pores) and equilibrium (adsorbents have different affinities to accommodate different species) [20]. Depending the nature of these forces, the adsorption can be classified into two general types:
Physical adsorption or physisorption: Established interactions between the solid surface and the adsorbate are physical in nature (Van der Waals force), doesn’t share or transfer electrons, reversible process, with low heat of adsorption. Chemical adsorption or chemisorption: Established forces are true chemical bonds which makes the process irreversible. It occurs only on the active centers with high values of adsorption heats. Some factors that influence the adsorption of a given compound are presented in the Table 1.2:
Table 1.2. Influence factors on the adsorption Surface (A larger adsorbent surface gives greater absorption and greater adsorption). Pore size distribution (determine accessible Solid properties surface adsorption) and particle size of the adsorbent. Solubility of the adsorbate in the solvent, adsorbate structure (presence of functional groups promotes solid-solute interactions), Nature of molecular size of the adsorbate (affects the rate of adsorption) and adsorbate ionic nature of adsorbate (adsorbate net charge). 32 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Characteristics pH (determine concentration of hydronium and hydroxyl ions in the of the liquid medium, setting the degree of dissociation), temperature (increasing phase temperature generates a reduction in adsorption) and nature of the solvent (affinity of the solid by the solvent and adsorbate). Competition The presence of multiple adsorbates can influence the adsorption between capacity and processing rate. adsorbates
Different materials can be used as adsorbents, depending on the application, price, mechanical and chemical resistance, abundance, easiness to use, easy regeneration, adsorption capacity and surface area. Table 1.3. resumes general characteristics of some commercially available adsorbents: Table 1.3. Most common adsorbent materials Carbonaceous materials Activated Carbonic porous material made by treatment of charcoal with oxidizing charcoal agents or burning of carbonaceous materials impregnated with dehydrating agents, with high internal surface, removes residues at low concentrations [21]. Carbon Discontinuous carbon filaments with diameters ranging from 20 to 80 nm , nanofibers with an internal structure similar to graphite, also similar to nanotubes in (NFC) shape and dimensions, with variations in orientation of the planes [22]. Also with low expansion coefficients and good mechanical, electrical and thermal properties. There are 4 types of NFC, Platelet, Fishbone or Herringbone, Ribbon and Stacked cup. Carbon Long cylinders made from hexagonal graphite lattice, comprising one or Nanotubes more cylindrical and concentric layers of graphite with a 0.34 to 0.36nm (NTC) spacing. It can be synthesized by means of electric arc discharge (EAD), laser ablation (LA) and chemical vapor deposition (CVD) [22]. The structure of the NTC confers different properties such as hardness and stiffness, elasticity, heat resistance, and mechanical strength, specific surface area and high thermal stability. There are single-walled nanotubes (SWNT: Single Wall NanoTube) or multiple wall (MWNT: Multi Wall NanoTube). Carbon Materials synthesized by sol-gel method, where gravitational forces are xerogels negligible and interactions are dominated by short-range forces like Van der Waals and surface charges, showing Brownian motion [23]. Ordered Materials with ordered porous structure and a complex chemical surface mesoporous with high surface area [24]. carbons Clays Mineral grains of less than 2 μm diameter, formed by silicate and aluminosilicate minerals with sheet-like structures, with large surface areas that can absorb important amounts of 1. Introduction 33 water, having the property to change their volume by adsorption of water molecules or other polar ions (swelling). All clays attract water to the surface (adsorption) but some of them leading it into their structure (absorption)[25]. Bentonite Material with soapy properties and a structure of montmorillonite (phyllosilicates added in the form of flakes), composed of two sheets of oxygen and silicon tetrahedrons, and interlaminar spaces that can be occupied by different cations. The final properties depend on the production methodology [26]. Fuller's earth Clays with different mineralogical composition, mainly palygorskite, calcium smectite and/or sepiolite, are used in bleaching and oil refining [27]. Kaolinite Kaolin is the trade name for white clays. This clay have very low water adsorption capacity [25]. Hydrotalcite Anionic clay with magnesium atoms tetrahedrically coordinated to six hydroxyl groups, and some Mg2+ cations replaced by Al3+. Calcination temperature has a very important effect on hydrotalcites and causes changes in physical and chemical properties [28]. Sepiolite Natural and inert clay, with composition of hydrated magnesium silicate. The raw extracted mineral is subjected to a grinding and drying processes. It is a fibrous mineral with large surface area (900 m2/g), due to small particle size and porosity [17]. Other adsorbents Silicalite Zeolite with MFI structure type (tridimensional system with two types of channels), with average pore size of 0.55 nm, useful in petrochemical applications with an outstanding thermal and chemical stability [29]. Alumina There are many crystalline forms of alumina which can be achieved by
heating of various starting materials, it is made of aluminium oxide (Al2O3), having surface areas of 150 – 400 m2/g with mesopores [30]. Bioadsorbent Chitin is a N-acetyl-D-glucosamine linear polymer of high molecular weight Chitosan (abundant in fungal cell walls and crustaceans). Chitosan is derived from chitin by hydrolysis, used as metal chelating polymer and for water treatment processes in industries such as beer, wine and dairy [30]. Mixed Mixed materials are being developed to synergistically improve the materials properties of its components; like clays and carbon composites for
decontaminating effluents and gaseous separation of N2 and O2 [31].
A new alternative, economic and efficient to remove mercury from aqueous effluents has been investigated, using as a raw material waste byproducts from industrial or agricultural processes (lignocellulosic biomass), which is used as an adsorbent [32]. A summary of the typical mechanism involved in the mercury adsorption process are presented in Table 1.4. 34 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 1.4. Mechanisms used in mercury removal 4 Mechanism Description Complexation The metal attaches to the active centers onto the cell wall through or chelation chemical bounds forming certain complexes [33]. Physical The phenomena associated with Van der Waals forces, in this case the adsorption sorption is quickly and reversible [34]. Ionic It is the proper one of the divalent metal ions that are exchanged with ions exchange of the polysaccharides present in the biomass. The process is also fast and reversible [35]. Precipitation The mechanism is associated with the formation of a complex in the cell wall subsequently it is hydrolyzed [36].
The use of different biomasses in the removal of heavy metals such as mercury has been reported, below in Table 1.5. some examples are shown.
Table 1.5. Removal of mercury with residual biomass 5 Biomass Example Sorption Ho et al.[37], studied the behavior of mercury adsorption in aqueous Equilibrium of solutions, using arborecenses ferns. It was found that the adsorption Mercury onto capacity depends on the temperature. The maximum adsorption was Ground-Up Tree 26.5 mg/g at a temperature of 25°C. Fern Removal of This study proposes the use of eucalyptus bark (Eucalyptus Mercury using camaldulensis) as a bioadsorbent for the removal of Hg (II) in aqueous eucalyptus bark solutions. The performance variables studied were adsorbent dosage, ionic strength, stirring speed, temperature, solution pH, contact time, and initial concentration of the metal. The experiments indicated that the adsorption capacity was dependent on the operating variables and the process was strongly pH dependent. Kinetic measurements showed that the process was fast and uniform. Among the kinetic equations studied, the pseudo second order equation best described the process. The maximum adsorption was 33.11 mg/g at 20°C [38]. Studies of guava Biosorption of Hg (II) was investigated by the use of guava bark (Psidium powder. In the investigation a batch system was used, and the effects guajava) bark as of various parameters such as contact time, initial concentration, pH bioadsorbent for and temperature were analyzed. It was found that the elimination of Hg removal of Hg (II) is pH dependent, with maximum adsorption at pH 9.0. In the kinetic (II) study the pseudo-second order equation was the one that most adjusted the experimental data. The maximum adsorption was 3,364 mg/g reaching 80 min, it has been shown that the guava bark powder can be efficiently used as a low cost alternative for the removal of divalent mercury from aqueous solutions [39]. Sorption of The adsorption of Hg (II) in aqueous solution under variable conditions 1. Introduction 35
Hg(II) onto of contact time, metal ion concentration, adsorbent dose and pH was Carica papaya evaluated by Basha et al. [40]. The results indicate that the adsorption equilibrium was established about 120 min. The adsorption of Hg (II) was strictly pH-dependent, and the maximum removal of 70.8 mg/g was observed at pH 6.5. The kinetic data fit well into the kinetic equation of pseudo-second order. This work illustrates an alternative solution for the use of the papaya tree, which is discarded at the end of its useful life. Therefore, its use for the removal of heavy metals from contaminated water can be a novel and cost-effective alternative. Use of rice straw Rocha et al. [41], carried out adsorption experiments using rice ear as biosorbent as a biosorbent of Hg (II) ions in aqueous solutions at room for removal of temperature. To obtain the best adsorption conditions, the influence of Hg(II) ions pH and contact time was investigated. This adsorption process was fast reaching equilibrium before 90 minutes, with a maximum at pH 5.0. The maximum adsorption capacity of Hg (II) metal ions was 0.110 mM/g. In addition, an excellent result was shown with the use of the ear of rice as bioadsorbent of metallic ions of mercury in industrial effluents. Removal of Ceiba pentandra (Ceiba), Phaseolus aureus (Jewish) and Cicer mercury from arietinum (chickpea), are trees and plants that grow in India, mainly in aqueous high temperature areas. The shell of the ceiba, jewish and chickpea solutions using crop wastes, are agricultural residues that can be used as waste from bioadsorbents in aqueous solutions [42]. Ceiba This study was carried out in a batch process, and the influence of pentandra, parameters such as pH, contact time, initial concentration of mercury Phaseolus ions and the adsorbent dose were analyzed. The experiments showed aureus and that the adsorption process corresponds to the pseudo-second order Cicer arietinum kinetic models. With an initial concentration of Hg (II) of 40 mg/l, a maximum removal of 25.88 mg/g was obtained for the ceiba, 23.66 mg/g for the jewish and 22.88 mg/g for the residues of Chickpea. Decontamination treatments of water-dye systems Currently dye contaminated water is an important environmental problem with significant impact due to their high toxicity and the wide spread use of dyes in industry. Nowadays, more than 100.000 types of dyes are available worldwide and more than 50% of them
-3 have very low lethal doses (LD50) around 2x10 mg/kg [43]. Raising up the challenge to develop efficient water treatment processes.
Printing, photographic, textile and paper industries are major dye pollutant industries, generating the need for appropriate management of water waste, including treatment and disposal systems. In order to oversee the legislation and actions to control and prevent 36 Wastewater treatment using an iron nanocatalyst supported on Fique fibers dye contamination in water sources the Ecological and Toxicological Association of Dyes and Organic Pigments Manufacturers (ETAD) was created in 1974.
Today, different treatments are applicable to industrial wastewater, these can be physical (the compound does not undergo transformation in its structure), chemical (there is a chemical change in the compound) and biological (use of microorganisms to remove contaminants). Conventional treatments that have been used are described in Table 1.6. Table 1.6. Conventional treatment for water decontamination 6 Chemical oxidation [44] Incineration Pollutant concentration is sufficiently high and the waste require high temperatures up to 800°C. Non catalytic Oxidation with dissolved oxygen from air or oxygen-enriched gas wet air streams, is used to create hydroxyl radicals as oxidizing agents. oxidation: WAO Catalytic wet Complete mineralization of organic contaminants with inorganic air oxidation: compounds such as ammonia and cyanides, using air or oxygen as CWAO oxidizing agent, improves process costs. Supercritic Oxidation by air (enriched or not in oxygen) at high temperatures wet air (250-400 °C) and high pressure (200-300 atm). The water/air fluid oxidation: acts as a single phase, at industrial scale makes a total mineralization
(SCWAO) of organic pollutants (conversion to CO2 y H2O), process with high costs. Advanced oxidation process (AOP) [45] Homogeneous Ozonation in The decomposition of ozone in water increases, generating the alkaline oxidation of organic pollutants in a direct way (reaction between the medium organic molecule and dissolved ozone) and indirect way (hydroxyl radicals are oxidants). Ozonation Hydrogen peroxide combined with ozone generate the decomposition, with hydrogen forming one mole of hydroxyl radicals per mole of ozone decomposes. peroxide Fenton The reaction of hydrogen peroxide with transition metals (iron), (Hydrogen generates highly reactive radicals (hydroxyl). It is used for treatment peroxide and of pollutants such as phenol, formaldehyde, BTEX (benzene, toluene, catalyst) ethylbenzene and xylene) and pesticides. Ozonation Is carried out by an electric discharge field as in the CD-type ozone and UV generators (corona discharge simulation of the lightning), or by irradiation ultraviolet radiation as in UV-type ozone generators (simulation of the ultraviolet rays from the sun). Electro- Oxidative capacity of hydrogen peroxide increases in acid medium as Fenton salts containing Fe+2 can regenerate the catalyst from Fe+3. 1. Introduction 37
Hydrogen The rate of photochemical reactions with organic matter can be peroxide and increased with the addition to ozone, hydrogen peroxide or both. UV irradiation Photo-Fenton Production of hydroxyl radicals by Fenton's reagent and UV irradiation, promotes Fe (III) complex formation, allowing regeneration of the reduced form of the catalyst. Electrochemic Use electrical power to break the bonds of molecules, electrons are al oxidation transferred to the organic compound. Heterogeneous
Catalytic Use of transition metal oxides (MoO3, TiO2, Cr2O3), supported metals
ozonation on oxides (Cu/Al2O3, TiO2/Al2O3), granular active carbon (GAC) and mesoporous systems (silicates MCM or SBA). Photocatalytic Photoexcitation of a solid semiconductor as a result of absorption of ozonation electromagnetic radiation, generating excitation of electrons in the valence band of the solid, causing the formation of voids characterized by a very high oxidation potential. Membranes [46] Semi-permeable physical barriers separating two phases, prevents their intimate contact and restricting the movement of molecules, having the capacity to provide high flows of permeate and manufacture in compact and in some cases in inexpensive devices.
The large flows of contaminated water necessary to treat in both cases, Orange II and/or mercury, required catalysts/adsorbents materials that must be easily to remove from the decontaminated water, then, heterogeneous catalysis have been extensively applied in industrial applications because of their straightforward separation, which often results in lower operating costs. Under this consideration a solid catalyst/adsorbents material becomes an interesting option for this application and therefore it is important to define the type of support and active phase that these material will be made of.
Catalysts supports Currently there is a great interest in the use of renewable natural materials as solid catalysts supports and as adsorbent materials. Their use could contribute to the solution of several environmental problems, taking advantage of their physical and chemical properties such as low density, biodegradability, flexibility, high wear resistance and excellent thermal degradation.
Natural supports such as fibers are lignocellulosic compounds formed by cellulose, hemicellulose and lignin. Particularly cellulose, is a highly attractive material in the development of novel supported catalyst because its mechanical and chemical properties, 38 Wastewater treatment using an iron nanocatalyst supported on Fique fibers considered a "green" material and not least, presence of large number of hydroxyl groups which are chemically available for a huge number of different functionalizations, allowing the modification of the physicochemical properties according to the target application [47].
Figure 1.2. Details of the cellulosic fiber structure [36] 2
Figure 1.3. Molecular structure of hemicellulose [37]3
Figure 1.4. Molecular structure of Lignin [38] 4
In relation to the hemicellulose, is one of several heteropolymers, such as arabinoxylans, present along with cellulose in almost all plant cell wall. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with 1. Introduction 39 little strength. It is easily hydrolyzed by dilute acid or base as well as myriad hemicellulase enzymes [48], its molecular structure is shown in Figure 1.3.
Lignin is a group of complex organic polymers that form important structural materials in the support tissues of vascular plants and some algae, lignin is particularly important in the formation of cell walls, especially in wood and bark, because they provide rigidity and do not rot easily. Chemically, lignin is a cross-linked phenolic polymer [49], its chemical structure is shown in Figure 1.4.
Several methods have been reported to prepare cellulose nanofibers from plants as Jute, Sisal and Kenaf [39 - 41]. Based on the mechanisms of fiber preparation, they can be classified in three groups: chemical, enzymatic and physical extraction methods, as presented in Table 1.7 [53].
Table 1.7. Methods of cellulose fibers preparation 7 The nanorods may be homogenized cellulose pretreated with an acid solution of microcrystalline cellulose (MCC). Some other cellulose fibers of Chemical approximately 200 to 400 nm long and 12 nm of wide, can be dispersed in preparation an organic medium of dimethylacetamide/lithium chloride (DMAc/LiCl) [54]. methods Another method is to disperse the cellulose (nanofibers) in water and to add the radical 1-oxyl-2,2,6,6-tetramethylpiperidine (TEMPO) in order to oxidate the wood pulp (Kraft). Some primary hydroxyl groups in polysaccharides including β-glucose in cellulose are selectively oxidized to carboxylate groups by TEMPO, with the advantage that oxidation mediated by TEMPO can be introduced in native cellulose, maintaining the fibrous morphology and crystalline characteristics [53]. Enzyme The bacterial cellulose of seaweed and ramie cotton can preferably preparation degrade by Trichoderma viride, turning waste into Iβ cellulose[55]. methods Nanofibers of 40 nm can be obtained, are used for reinforcement in composite materials based on polymers. Physical Mechanical processes can be done in a high pressure homogenizer. This preparation yield the division and disintegration of cellulose fibers and exposing methods smaller microfibrils and nanofibrils with diameters in the range of 10-100 nm[56].
40 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
An example of a lignocellulosic material is the Fique fiber (Furcraea andina), plant from the american continent, with more than 400 species reconigzed. It has fleshy fibrous leaves, with or without thorns. Fique plants have long roots, bloom once per year and with a size that varies accordimg to the specie. Since ancient times this plant have been known by the name of “Woderland Plant”, because the varies uses that have been given to it, including drugs extraction, production of fermented beverages, mops, among others [57].
Figure 1.5. Furcraea andina (Personal archive) 5
In Colombia fique crops are mainly located in the Andean region, in territories where the climate is temperate. The most relevant department in terms of fique production are: Antioquia, Boyacá, Cauca, Nariño and Santander [23]. In terms of other type of natural fibers, fique has mainly two competitors: Jute, a soft fiber used for packaging and textiles, and sisal which is a fiber used in cordage. However, the fique fiber has two advantages: it is not as soft as jute, but not as stiff as sisal [22].
Furcraea andina (Fique) plant, from the Agavaceae family Andina (see Figure 1.1), is characterized by an erect stem with an average height of 2 to 7 m and average width of 10 to 20 cm; the trunk made up of 75 to 100 leaves (1 to 3 m long), radial shape, fleshy, pointed, well-toothed and prickly; with greenish-white flowers "margüey" only that bloom once a year. Fique has a lifespan of 10 to 20 years and a production peak of 3 to 6 years [58]. Table 1.8 resumes an average weight distribution of the fique leave components, their usable percentage and some of their applications:
Table 1.8. Average weight distribution of the fique leave components, usable percentage and applications [59] 8 Part Leaves Useful percentage Uses weight (%) (weight %) 1. Introduction 41
Fiber 5 4 Textile industry, packing Juice 70 40 Extraction Tow 8 3 Paper pulp Marc 17 10 Construction materials
Fique leaves undergo a defibration process (operation that separates the bark from the inner fiber) in a shredder machine. Defibration is the initial step in the transformation of fique leaves. The several byproducts obtained have a wide range of applications, as summarize in Figure 1.6 [59].
Long fiber Chaff Juice
Packing Paper Surfactants
Fiber- Agromants Detergents reinforced
Stuffing Cosmetic Cordage mattresses products
Thermal Crafts Alcohol insulation
Organic Textils Bioinputs fertilizers
Figure 1.6. Potential uses of the products resulting from fique [58] 6
Long fibers only constitute 4% (weight) of the fique leaves and form the main structure of the cell walls, mainly composed of cellulose, hemicellulose, lignin and pigments; each fiber filament is composed of fibrils bonded together by lignin. An average chemical compound weight distribution of fique fiber filaments is presented in Table 1.9.
Fique fiber and its byproducts could become excellent raw materials in various chemical and physical processes due to its compatibility with several materials and its outstanding mechanical properties (torsional strength, bending and tensile) [60].
Table 1.9. Main components of fique fiber [58]9 FIBER Weight % Ashes 0.7 42 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Cellulose 73.8 Ream 1.9 Waxes and fats 1.9 Lignin 11.3 Pentosanes 10.5 TOTAL 98.2
In order to classified fique fiber, ICONTEC has developed a technical standard procedure (NTC 992) that regulates the quality of natural fibers in Colombia, including definitions and classification, setting the humidity and fiber length requirements [61]. Table 1.10 resumes some of fique fiber characteristics use to determine fique fiber quality.
Table 1.10.10Fique fiber quality standards classification [59] SORT OF FIQUE CHARACTERISTICS - Good defibration - Length greater than 90 cm Fine - Spall: low - Free of knots and tangles ropes - Free of diseases and pests - Variable color - Regular defibration Ordinary - Length greater than 90 cm - Free of knots and tangles ropes - Variable color - Good to regulate defibration - Length lower than 90 cm Short - Free of knots and ropes - Possible entanglements - Variable color
Fique long fibers have been used in the production of textile fabrics, threads, cordages, packaging and crafts. Particularly in Colombia, the production of added value fique fiber products is not well developed, although is an important job generator in some regions, the economic gain margin is low; a fine quality fiber has a marked value in the order 1230 COP/kg meanwhile a low quality fiber has a marked value in the order of 1100 COP/kg, reducing the incentives for an appropriated production of the fiber [59].
Some companies responsible for the production of packaging materials made up of fique fiber are Cohilados del Fonce LTDA (San Gil), Compañía de Empaques S.A (Medellín), Empaques de Cauca S.A (Popayán) and Hilanderías Colombia LTDA (Pasto). 1. Introduction 43
Currently, the fiber is used by Colchones Spring, Colchones El Dorado and Americana de Colchones, to produce fique sheets as a new material called “microlink ®”, which is a fiber agglomerate of fique and cotton, used as thermal insulator and structural reinforcement of mattresses, it has been an innovative application of this natural product taking advantage of the excellent strength, flexibility and thermal insulation of fique fiber [58].
Some recent studies have shown that the use of fique fiber for the design of reinforced materials is an excellent alternative due to its biodegradability, diversity, renewability, recyclability, wide availability, low energy consumption in manufacturing, competitive cost (low cost per unit volume), low density and mechanical properties; even if after its lifespan is over and recycling is not an option, production of renewable energy by incineration is an available alternative [62].
Several studies have reported the mechanical effects of using fique fiber as reinforced materials in composite materials. Latorre et al. [63], prepared an epoxy polymer matrix reinforced with fique fiber used both as a protection and reinforcement of dented and light corrode pipelines. This material stopped corrosion progress and presented excellent adhesion to the pipeline surface, resistance to cathodic processes and mechanical strength. Hidalgo et al. [62], reported a 212% increment of the mechanical strength and a 218% increment on elasticity for composites made out short fique fiber and LDPE (low density polyethylene). Contreras et al. [64], used fique fiber as a reinforcing material in polyester matrices and evaluated the strength, flexibility and impact resistant of the produced matrices, concluding that fique fiber is an excellent alternative to replace synthetic fibers, but also highlighting that imperfections such an uneven fiber diameter and fiber impurities could decrease the quality of the products by acting as stress concentrators. Hybrid materials made out of fique fibers, fiber glass and polyester resin have been explored as a suitable material for the production of autobuses bumpers (Paredes et al. [65]), finding that fiber length is the most influential parameter in the mechanical performance of the hybrid material. Gañan et al. [66], studied the crystallization process and thermal degradation of a thermoplastic polypropylene matrix reinforced with fique fibers. The study found that the reinforcing material provides enhanced thermal stability.
Other studies have explored not only the mechanical properties of fique fiber but also have investigated its chemical properties in order to use the fiber as an adsorbent material, catalyst support and some other applications. Gañan et al. [66], evaluated by FTIR- ATR, 44 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
SEM and TGA the effect of chemical treatment such as mercerization and salinization on raw fique fiber. Deposition of metallic particles on modified fique fiber surfaces was reported by Castellanos et al. [67], particularly gold nanoparticles were synthesized using 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHTAC) as cationization agent in strong alkaline conditions (NaOH). The study found that the molar NaOH/CHTAC ratio has not significant influence on the size and distribution of the gold nanoparticles, it was also determinate that the cationization process improved the fiber mechanical properties. Some other type of nanoparticles has been explored, Chacón et al. [68], studied the degradation of organic dyes on nanostructured MnO2/fique fiber catalysts, finding that Coulomb interaction play a major role on the attachment of the MnO2 particle to the fiber surface. Nanoparticle formation on the fiber surface was corroborated via FESEM. The synthesized catalyst was very active in the degradation of indigo carmine dye, reaching degradation values as high as 98% in less than 5 minutes.
Currently an increasing tendency in the world is to move back into the use of renewable raw materials free of chemicals and not harmful to human health. To continue in this path, it is important the implementation of policies that contribute the implementation of elements for sustainable development, soil and water use, among others. Nowadays in Colombia, there is an interest of the entities and institutions implicated in the fique fiber chain production to find added values applications involving green chemistry and designing cleaner production processes [34].
Iron nanoparticles Nanotechnology applied in the improvement of water treatment processes has become an important tool in environmental catalysis because it could provide innovative technical solutions to control emissions, reducing the impact of existing technologies, eliminating no- biodegradable molecules and disabling the most resistant organisms and potentially creating new processes.
Nanomaterials could be very reactive because of its large surface area relative to volume, and because the presence of a greater number of reactive sites. These properties allowed more contact with pollutants, increasing reaction rates. Also, taking advantage of their "nano" size; they can be impregnated on very small spaces, allowing particles to travel farther, improving dispersion [69]. Silver, zinc oxides and iron oxides nanoparticles have been used to carry out water purification of E. coli and arsenic [70]. Dufour et al. [71], 1. Introduction 45 developed filters that act as a ceramic "sponge" (prepared with natural clay), to retain pollutants from textiles and domestic industries, this type of materials have the advantage of being easy to manufacture, clean and reuse [70].
Studies conducted at Rice University, found an alternative to the water treatment of effluents polluted with arsenic by taking advantage of the magnetic interactions of iron oxide nanoparticles with carefully placed magnets. This significantly reduces the environmental and health impacts [72] and allows to perform environmental risk assessment in terms of toxicity, exposure and risk characterization [73].
Nanostructured catalysts have been also applied in the destruction of chlorinated organic contaminants in water by using low concentrations of bimetallic core/shell nanoparticles, taking advantage of a synergetic catalytic effect of gold nanoparticles coated with palladium [74].
Nanostructured catalyst based on TiO2 also have been developed for photocatalytic decontamination of water, this approach can be classified in three groups: the first group is the use of pure TiO2 nanomaterial (first generation), where the more relevant catalytic variable is the size of the TiO2 particle; the second generation corresponds to the metallic doping of TiO2 to incorporate impurities in the crystal structure in order to increase the radiation absorption capacity of TiO2, and the third generation of TiO2 based catalyst but doped with nonmetals such us sulfur-doped TiO2 [75].
Another compound which has been used for the synthesis of nanoparticles are iron oxides, in the forms of magnetite (Fe3O4), maghemite (γ-Fe2O3) and hematite (α-Fe2O3) are the most common [76]. A nanometer scale this compound has shown great properties as biocompability, size, large surface area, superparamagnetism and ability of surface modification [77].
Additionally, techniques that allow easy synthesis and properties control of iron oxides nanoparticles has been developed; increasing the versatility of the produced nanoparticles in terms of size distribution, morphology, surface chemistry and magnetism [78]. However, research continues in order to improve nanoparticle stability exploiting the possibility of iron oxide to react with different compounds, avoiding aggregation and sedimentation, increasing mobility and reactivity [79]. 46 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Based on the wide range of chemical and physical properties reported for oxide nanoparticles, many catalytic application have been proposed, such as adsorbents, enzyme immobilizers and wastewater treatments [80].
Today, novel applications for iron NP Fe0 are seeking greater flexibility in treatment, reuse treatment agents, environmental safety (sustainability), optimization of costs synthesis and modification, and very important, the possibility of scaling and easy separation [70].
However, the use of nano zero valent iron (nZVI) have found increasing applications in environmental technologies and hazardous waste treatment, owing to their superior reactivity, extremely small particle size and large surface area towards a variety of recalcitrant contaminants and their enhanced capacities for contaminant abatement [82].
Although much work was devoted to the metal sorption and reduction by nZVI particles, the exact contaminant removal mechanisms including the particle surface chemistry are still not fully understood [83]. In order to demonstrate a mechanism, the zeta potentials after the adsorption of Hg (II) ions have been measured, the surface charge of the adsorbent with nZVI after exposure to the toxic metals is approached to zero. It is believed that toxic metals as mercury is removed by the positive interactions between the negative charge of the immobilized nZVI and the positive charge of the mercury solution which eventually decreases the negative charge, due to the oxidation of Fe0 to Fe+2 and Fe+3 and also adsorption/reduction of Hg(II) ions on the surface of nZVI. Demonstrated chemisorption of Hg (II) ions onto supports with nZVI throughout the adsorption/reduction processes are in line with the obtained kinetic and adsorption isotherm data [84].
Aditionally, there have been numerous studies that have demonstrated the ability of iron oxide to remove contaminants from water effluents [77] these technologies are classified into two groups: a) technologies using nanoparticles as adsorbents or as immobilizers for improving removal efficiency and (b) using iron oxide nanoparticles as photocatalysts to break or convert pollutants to less toxic forms.
Then, the window is open to develop new science that contributes to sustainable solutions to a world that is beginning to recognize the need to remedy and fix the excessive damage that has been done to nature. Consequently, there is a need of implementing new technologies for the remediation of water sources; this research explore the development of a catalyst-adsorbent material containing iron species as the active phase and fique fiber 1. Introduction 47 as support, based on the facts that iron species are active for this kind of treatments and fique is a green removable material with very attractive physicochemical characteristics applicable in this type of processes.
References
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52 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
1. Introduction 53
54 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Chapter 2. Physochemical treatment and characterization of Furcraea andina
Abstract: A physicochemical pretreatment on the natural fiber fique (Furcraea andina) was evaluated in terms of the modification of the physical and chemical fiber properies, as an initial stage in the process of setting appropiate condition for its later use as alternative matrix in the synthesis of a catalyst for removal of heavy metals and dyes. The fiber was characterized structurally using the NREL methodology, determining the percentage of lignin, cellulose and hemicellulose, obtaining values of 22.58, 36.3 and 28.15, respectively. In addition, the pH of zero point of charge (pHzpc), the acidic and basic sites, humidity, total solid and ashes were measured. The studied physicochemical pretreatment seeks to expose and enable superficial sites (functional groups) that subsequently can act as centers of nucleation in the synthesis of nanoparticles. Exposure of functional groups was performed by means of a procedure assisted with ultrasound, varying the sonication time (30, 60 and 90 min) finding 60 minutes of pretreatment as the most beneficial, evidencing an increment of cellulose and reduction in the percentage of lignin and hemicellulose. Subsequently, chemical activation of the sonicated fiber was held at different times of functionalization (1, 2 and 3 hours) in cycles of acid-base treatments, Fourier transform infrared spectroscopy (FTIR) - attenuated total reflection (ATR) and Energy-dispersive X- ray spectroscopy (EDS) equipment coupled to a SEM probed that 3 hours of treatment is the time with the highest impact in terms of surface functionalization and the same time, the deposition of the sodium ions was verified. X-Ray Diffraction (XRD) was used to determine the fiber crystallinity in all stages of the pretreatment; crystal size in the final stage was 5 nm on average. Total surface area was improved by the pretreatment and it was determinate applying the BET method by N2 adsorption isotherms. Scanning electron microscope (SEM) micrographs showed in the pretreatment stage a fiber clean and free from waste from the defibration process and a superficially more homogeneous fiber for the functionalization stage. Finally, the thermal characterization by thermogravimetric 2. Physochemical treatment and characterization of Furcraea andina 55 analysis (TGA), revelaled a futher effect of the funtionalization process when compare with raw and pretreated fiber samples.
Keywords: Furcraea andina spp, pretreatment, functionalization, treatment wastewater, catalyst.
Introduction Due to its mechanical and chemical properties, cellulose is a highly attractive natural material, especially for the presence of a large number of hydroxyl groups useful to perform a tailor made chemical functionalization and then provide specific physicochemical properties according to the desirable application. Pretreatment and functionalization processes with close control over the effects on the cellulose structure can help to improve its properties (crystallinity, length, width and aspect ratio), producing materials with a wide spectrum of applications, such as catalysts support and absorbing material, among others, having the aditional advantage of being environmentally friendly.
Chacón Patiño et al.[1], Wang et al.[2], and Chattopadhyay [3] have shown that the development of technological applications from cellulose is a good alternative for the generation of materials with enhanced chemical, mechanical, thermal and catalytic properties. Among available vegetable materials with high percentages of cellulose, fique fiber presents exceptional properties in comparison with some widely used synthetic polymers: this fiber is biodegradable, flexible, low cost, low density, with excellent thermal and mechanical properties. In addition, as a social impact, fique provides employment to about 70,000 families, contributing in some important areas to the substitution of illicit crops in Colombia [4].
The goal of this study was to performe a complete characterization of the raw natural fique fiber monitoring the effect of three different physicochemical pretreatments on the surface chemistry, morphology and textural properties, crytalline structure and structural properties, following the Nationational Renewable Energy Laboratory (NREL methodology) [5]. The later, in order to find the pretreatment conditions that provide enhanced properties to the fique fiber to be used as a catalytic support for the synthesis of nanoparticles. 56 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Materials and methods
Materials Raw fique fibers standardized in moisture, color, length, width, free of knots, diseases and pests was provided by Compañia de Empaques S.A, who collects it from the Colombian coffee region.
Fiber pretreatment In order to removed lignin, hemicellulose, carbonates, chlorophyll, saponins and any other waste present, a physical process (ultrasound) was performed;ultrasonic pretreatment has been also reported to decrease cellulose crystallinity and increase lignocellulosic material porosity [6]. 1g of raw fiber was submerged in a ultrasonic bath using an erlenmeyer containig 200mL of deionized water (0.054 μS), sonication time was performed at three different levels (30, 60 and 90 minutes, called M30, M60 and M90 respectively) at 42 KHz and 100 W. After sonication the fibers were removed from the deionized water and dried overnight at room temperature. The effect on the fiber structure in this process was assessed following the NREL methodology for the determination of structural carbohydrates and lignin in biomass [5].
Fiber functionalization Functionalization of surface cellulose exposed during the ultrasound pretreatment was performed following the procedure proposed by Wang et al. [2], The pretreated fiber was placed in 200mL of HCl (5% vol.), varying exposure time at three different levels (1, 2 and 3 hours) at room temperature, then the fiber was rinsed with distilled water. Finally, the fiber was placed in 200mL of NaOH (6% vol.) at 60°C also at three time levels (1, 2 and 3 hours. Called MC1, MC2 and MC3 respectively)), then rinsed with distillate water and dried at 80°C for 12 hours. Each experiment was performed in duplicate and the results for each time of functionalization were averaged.
Figure 2.1 section a, ilustrates the initial step of functionalization on the pretreated fiber by immersion in HCl, causing acid hydrolysis of the polymeric chains of cellulose and breaking intermolecular hydrogen bonding, and superficially degrading cellulose to form hydroxylated surfaces [7].
2. Physochemical treatment and characterization of Furcraea andina 57
The second step of the functionalization mechanism (Figure 2.1b) is achieved by exposing the previously formed hydroxylated surface to NaOH as cationic agent, promoting the
+ formation of the corresponidng salts (RCH2ONa ) on the fique’s surface and cationizing the fiber [8].
The chemical surface functionalization process performed on the pretreated fique fiber allows the formation of cationic sites capable to chemically interact with a variety of chemical elements and compounds, such as the incorporation of innorganic nanoparticles [3, 9].
Figure 2.1. Route used for functionalization of pretreated fique fiber 7
Characterization
Humidity Humidity of raw and pretreated fiber was determinate on 1g of fique using an infrared radiation scale (PMB53-Adam) for 25 minutes, at 100°C; samples have not undergone any other treatment previously to the humidity determination experiment.
Chemical structural components The NREL [5] methodology was implemented for the determination of structural components in the fique fiber. This uses two acid hydrolysis steps to fractionate biomass. The first step allows the determination of the acid insoluble lignin in the sample (via 58 Wastewater treatment using an iron nanocatalyst supported on Fique fibers standarized gravimetry procedures). The acid insoluble residue was placed in a crucible and loaded in a oven at 105°C (Labtech Essa) until constant weight, then the samples were removed from the oven and cooled in a desiccator and their weight was recorded; finally, the crucibles and residue were placed in a furnace (Thermo Scientific Lindberg/Blue Moldatherm™) at 575°C for 24 hours, the weight of cold samples were recorded again. The second step used UV-Vis spectroscopy to determined acid soluble lignin, the absorbance of a hydrolysis aliquot was measured at wavelength of 320 nm using as blank a solution of sulfuric acid 4%(v/v).
A second stage of the NREL characterization involves the fragmentation of the fibers into soluble monomerics forms (glucose, xylose, arabinose and acetic acid) and quantification using HPLC chromatography (VWR - HITACHI ELITE Lachrom system, consisting of a model L-2130 quaternary pump and a IR detector, Model Shodex RI - 101). A stainless steel Shodex SC1011 (300 x 8 mm I.D.) was used in the analysis. A gradient method with HPLC grade water, filtered and degassed as mobile phase was employed in the separation. Elchrom Elite software Chromatography data system was used for data processing and reporting. The injection volume was 20 µL each time to achieve reproducible injection, which was conducted with automatic injector (Model L-2220). The flow rate was kept at 0.6 ml/min during the run and the temperature was kept at 85°C in the separation column. Peak identities of the degradation products were confirmed by both retention time and spectra matching of standard compounds.
Surface characterization One of the goals of the treatment and functionalization processes is to modified both the physical and chemical properties of the fiber surface, as the chemical environment of the fiber surface is modified, properties such as the pH of zero point of charge and the acidic and basic surface sites change too.
Determination of the pH of zero point of charge (pHzpc) was obtained using a drift method, solutions with 45mL of KNO3 (1% vol.) were adjusted to an initial pH in the range of 2 to 10 by adding HCl 0.1M or NaOH 0.1M, the volume of each solution was completed up to
50mL by adding KNO3 (1% vol.) Once the pH of the solutions were set, 0.1g of fique fiber (raw, pretreated or functionalized) were added and the suspensions were stirred for 24 hours at 25°C and then the pH of the supernatants were registered [9]. 2. Physochemical treatment and characterization of Furcraea andina 59
Acidic and basic surface sites were determined by the Boehm titration method [10]: 1g of fique fiber (raw, pretreated or functionalized) was added to 50 mL of 0.1M NaOH (for acid sites determination) or 0.1M HCl (for basic sites determination) solutions, stirred for 5 days at 150 rpm and 30°C, then a 10 mL aliquot from each suspension was titrated with standard solution; pH registry was performed up to a total volume of 25mL of standard solution added.
Fourier Transform Infrared Spectroscopy (FTIR) was used to identify changes in the fiber functional groups at different stages (raw, pretreated and functionalized). All samples were left at room temperature overnight before being analyzed. FTIR were determined using an ATR (PIKE) diamond crystal accessory at an angle of 45° attached to a FT-IR Nicolete iS 10 spectrometer (Thermo Fisher Scientific). Scans of 20 readings were performed by spectrum; the data were recorded from 4000 to 600 cm-1.
Additional superficial chemical information of the fiber was obtained using Energy- dispersive X-ray spectroscopy (EDS) equipment coupled to a SEM, this type of chemical elemental analysis was performed in a Zeiss Auriga FIB-SEM (GeminiSEM) attached to the Oxford INCA EDS equipment with MAX80 SDD detector system, operating in spectrum collecting mode under high vaccum conditions, 20kV and approximate at a 5mm of working distance.
Structural characterization
Crystalline information of fique fibers was measured at room temperature using a XPert Pro MPD diffractometer with monochromator of crystal graphite using Cu Kα (λ = 1.5406 Å) at 40 KV and 30 mA. Diffraction patterns were obtained in the range of 2theta =10-40°, with a step size of 0.02° and measuring time of 50s per step. Experimental data was analyzed using PANalytical X'Pert HighScore Plus database.
Morphological and textural characterization
The total surface area was measured by the adsorption of nitrogen (N2) at 77 K, using a
Quantachrome NOVA e-Series surface area analyzers. N2 isotherms were performed on fique fiber samples at different stages of treatment (raw, pretreated and functionalizated);
o before N2 adsorption was performed on the samples they were degased at 80 C for 8 hr; the calculation of the total superficial area was done using the BET method [11]. 60 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Morphologycal characterization of fique fibers was achieved via Field Emission Scanning Electron Microscope (FESEM) performed on thin film gold coated samples using a Zeiss Auriga FIB-SEM (GeminiSEM) scanning electron microscope, coupled to a secondary electrons (SE2) detector. The micrographs were taken at 1.5 kV, working distance (WD) ranging from 4.9 to 5.2 mm, at different magnifications.
Thermal characterization Thermal gravimetric analysis (TGA) was performed to compare the thermal stability of each sample, TGA analysis was performed using a thermogravimetric analyzer (TGA1, Mettler Toledo), in a temperature range from 25 to 580oC at a heating rate of 5ºC/min in an
-1 inert atmosphere (N2, flow of 50 mL.min ).
Results and discussion
Fiber pretreatment Table 2.1 summarizes the proximate analysis, the structural carbohydrates and lignin results of raw and pretreated fibers. There is an evident increase of the fiber humidity after pretreatment, reaching a maximum value of 11.24% at 60 minutes of pretreatment. This kind of behaviour has been previously reported, suggesting that a higher content of water in the fiber constitution facilitates the movility of chemical structures, improving structural reorganization in the fiber and increasing crystalline cellulose [1].
High moisture content have been reported to be related to the formation of carboxylic functional groups (-COOH), increasing fiber swelling via an osmotic effects and increasing the affinity with water -OH groups, giving the fiber a hydrophilic character. Water retention has been also reported to be an indicator of increased fibrillation of the treated fiber [12].
Fique fiber sonicated for 60 minutes, reported a wet basis moisture content of 7.43%, showing a reduction with respect to the humidity of all pretreatments accordingly to the functionalization made, chemical treatment reduces the number of –OH. The acid insoluble residue (AIR) declined sharply, indicating that the longer the pretreatment the smaller the presence of insoluble residue in the composition of the fiber [13]. Ashes weight percentage decreases with the pretreatment time, presenting a small reduction after 30 minutes, but reducing in a dramatic way after 60 minutes, meaning that sonication may have a major impact in the removal of inorganic substances that could be present in the 2. Physochemical treatment and characterization of Furcraea andina 61 raw fique [14]. Peinado et al.[4], reports a value of ashes of 0.7% for fique fibers from the Santander region (north east of Colombia), different to the value obained for the fique used in this study (0.94%), such differences in raw fique are ussually relate to non comparable agriculture procedures and conditions that varied from region to region [4]. Total solids decreased with increasing time of sonication, mainly due to the change in the percentage of moisture (Table 2.1).
Table 2.1. Fique fiber proximate analysis and structural carbohydrates and lignin (NREL) analyses 11 Component Weight Percentage (%) Raw M30 M60 M90 Humidity 2.10 7.92 11.24 10.34 Total solids 97.90 92.08 88.76 89.66 Acid insoluble residue (AIR) 23.02 14.31 13.48 8.41 Ashes 0.94 0.83 0.04 0.02 Lignin 22.58 13.92 13.94 8.91 Hemicellulose 28.15 33.49 27.21 30.46 Cellulose 36.33 45.08 41.42 44.56
Also there is a reduction in the content of lignin of the pretreated samples at any of the pretreatment times: 8.66% for 30 minutes, 8.64% for 60 minutes and 13.67% for 90 minutes. Table 2.2 summarizes the contribution of insoluble and soluble lignin determined using NREL methodology, being insoluble lignin (AIL) the most abundant type of lignin found in the sample.
Several studies have reported that lignin constitutes between 10 to 25% of the cell wall in most natural fibers [16], the value obtained for the samples studied in this work was 22.58%, a considerable larger value to the ones reported by Peinado et al.[4], and Chacón et al. [1], of 11.3 and 14.5%, respectively (Santander region fique).
Table 2.2. Lignin content in fique fiber pretreated at different times 12 Component Weight Percentage (%) Raw M30 M60 M90 Acid insoluble lignin (AIL) 22.08 13.47 13.44 8.39 Acid soluble lignin(AIS) 0.50 0.45 0.51 0.51 Total lignin 2.58 13.92 13.94 8.91
62 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
During the hydrolysis, polymeric carbohydrates are hydrolyzed into monomeric forms, which are soluble in the hydrolysis liquid. They are then measured by HPLC, the concentration of the polymeric sugars are calcuated from the concentration of the corresponding monomeric sugars obtained by HPLC, using a correlation between C-5 sugars (xylose and arabinose) with the hemicellulose and a correlation between C-6 sugars (glucose) with cellulose [5].
In terms of hemicellulose there is not a clear tendency of the effect of the pretreatment. Initially after 30 minutes of pretreatment, the hemicellulose weight percentage increases from 28.15 to 33.49% then reduces to 27.21% after 60 minutes to finally increase to 30.46% after 90 minutes, this kind of behavior has been previously correlate to a mechanism where after an initial disrruption of microfibrils they associate into clusters or bundles denominate macrofibrils [15]. Raw fique fiber hemicellulose composition of 28.15% is within the 15 to 30 weight % range reported by other authors as Saha [18].
All the pretreatment times increased the weight percentage of cellulose in the fiber, obtaining the highest value for 30 minutes of pretreatment (45.08%), confirming the positive effect of sonication treatment on the fiber. This kind of behavior has been reported to be caused by the destructive effect that sonication has on hemicellulose and lignin since produce glycosidic bonds dissociation, promoting the formation of weaker oligosacharides and reducing the molecular weight [19].
The main constituent of wall cells in plants is cellulose. Fique analyzed in this study has a 36.3% of cellulose in its composition, very different from the value reported by other authors as Peinado et.al [4], and Chacón et al. [1], (73.8% and 63%, respectively). Some authors have attributed this difference to the type of fertilizer used during cultivation, no comparable defibration process, different species of fique plant and even environmental conditions of each region [20].
Table 2.3 reports the increment in glucose content for the different sonication times, due to the increase of cellulose exposition as final aim of this pretreatment. 30 and 90 minutes pretreatment times showed a small increase in xylose, however at 60 minutes xylose decreased; this type of behavior was also observed for hemicellulose, confirming the directly proportional relationship between xylose and hemicellulose. The insignificant change in arabinose and acetic acid values indicates that the sonication had a neglectable effect on these compounds. 2. Physochemical treatment and characterization of Furcraea andina 63
Table 2.3. Carbohydrates present in raw and pretreated fique fiber 13 Molecule mg/mL Raw M30 M60 M90 Glucose 0.212 0.249 0.222 0.228 Xylose 0.073 0.084 0.070 0.079 Arabinose 0.058 0.058 0.058 0.058
During the sonication treatment, energy is transferred to the cellulose chains by cavitation, gradually disintegrated hydrogen bonds. However, the complexity of the fique fibers multilayer structure limits the impact of the pretreatment mainly to lignin [21] and hemicellulose [22], thereby increasing the exposure of cellulose and the porosity of the fiber due to the division of fibrils on the longitudinal axis [23] and creating around the cellulose structure repulsion forces keeping microfibrils from aggregation [6].
Based on the results obtained during the pretreatment of raw fiber, the M60 pretreatment was selected and samples exposed to this treatment are the ones used in the process of functionalization .
Fiber functionalization
Surface characterization Figure 2.2 shows the pH curve used to determinate the pHzpc of the raw and pretreated fique fibers. The raw fiber (blue dots) presents an intercept with the zero value of the abscisa at 5.32 indicating an acid behavior most probably due to the presence of different ionizable functional groups such as carboxylic, phenolic, alcoholics and hemiacetal groups [24], contained in the macromolecules of hemicellulose, lignin and cellulose.
64 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
8
6
4
2
∆pH 0 0 1 2 3 4 5 6 7 8 9 10 -2 Raw -4 Pretreated Functionalized -6 pHi Figure 2.2. pHzpc for the fiber according to treatment 8
For the fiber pretreated by ultrasound (M60) (orange dots), the pHzpc decreased to 4.18, indicating that pretreatment makes the fiber more acidic by the partial removal of lignin and hemicellulose, exposing more acidic functional groups on the surface of the fiber, feature which is characteristic of cellulose. This result is an indication of the positive effect of the pretreatment on the fiber surface, depending on the method used in the synthesis of nanoparticles these activated groups serve as nucleation sites for the formation of nanoparticles. The functionalization process increased the pHzpc of the pretreated fiber to 8.23 (gray dots), indicating that the adsorption of cations on the surface of the pretreated fiber was achieved satisfactorily, fulfilling the purpose of functionalizing the fiber, increasing the number of positive charges on the fiber surface and creating the conditions for an appropiated functionalization process.
In Figure 2.2 the raw, pretreated and functionalized fiber, at pH equal to 2 have a similar behavior attributed to the presence of carboxyl groups content of cellulose and their degree of dissociation. About 90% of the cellulose carboxyl groups are dissociated at pH 5, at higher pH values the degree of carboxyl groups dissociation is even higher, but the dissociation degree as a function of pH does not follow the theoretical curve, particularly, at pH = 2, cellulose fibers become neutral. Therefore, the cationic retention depends on the pH [25].
The quantification of acidic and basic sites by the titration method Boehm [10] (Table 2.4) fit very well with the results obtained in the zero point charge characterization. There is an increase in the acid sites when the raw fiber is pretreated which has been reported to be 2. Physochemical treatment and characterization of Furcraea andina 65 related to a greater presence of carboxylic, cyclic anhydrides, lactones, and phenolic hydroxyl groups [26].
The surface sites were calculated in miliequivalents of titrant solution using equation (1). Consequently, the difference between initial moles of HCl and moles of HCl consumed by NaOH titration represents the amount of acidic sites on fique fiber and the difference between initial moles of NaOH and moles of NaOH consumed by HCl titration represents the amount of basic sites on fique fiber, as expressed in equation (1) [27]:
푉푡푖푡푟푎푛푡퐶푡푖푡푟푎푛푡 − 푉푎푛푎푙푦푡푒퐶푎푛푎푙푦푡푒 푆𝑖푡푒푠 = Eq (1) 푆푎푚푝푙푒 푤푒𝑖𝑔ℎ푡
Where Ctritant, Vtritant and Canalyte, Vanalyte are the concentration and volume of the titrant and analyte solution, the sample weight represents the dry weight of fique fiber before the procedure (raw, pretreated or functionalized) subjected to the titration.
Table 2.4. Results of the acidic and basic sites in the fique fiber in different stages of analysis 14 meq/g Sites Raw Pretreated Functionalized Acids 0.700 ± 0.141 0.750 ± 0.035 0.100 ± 0.071 Basics 0.050 ± 0.000 0.075 ± 0.035 0.775 ± 0.035
The surface of functionalized fiber has an increase in the basic character, with an increase
in the number of basic sites and a minimum amount of acid sites. Transmittance (u.a) Transmittance
3800 3450 3100 2750 2400 2050 1700 1350 1000 650 Wavenumber (cm-1) Raw M30 M60 M90 MC1 MC2 MC3 Figure 2.3. FTIR - ATR spectrum of raw fique fiber, pretreated (M30, M60, M90) and functionalized (MC1, MC2, MC3) between 4000 and 600 cm-19 66 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Figure 2.3 presents the FTIR – ATR spectrum of the raw, pretreated and funtionalized fibers. The spectrums show a significant change in the region between 3600 and 3200 cm- 1 where the OH groups are identified; also there is a noticeable decrease in the intensity of the signals in the region between 1800 and 1500 cm–1, which is usually regarded as an indication of water loss in the fiber and the disappearance of C=O chemical bonds [28].
The differences observed in the spectra located in a region of 2920 to 2850 cm-1, are related with the functional group CH2, present in the general chemical formula of monosaccharides like glucose, in this way it is evident that with the application of pretreatments as sonication and functionalization increases the number of exposed glucose, since they are the monomers constituents of cellulose [4]. The reduction in the intensity of the peaks located between 1780 and 1640 cm-1 correspond to samples that were exposed to longer pretreatment times and are related to an increase in the number of carbonyl functional groups (C = O) present as aldohexoses (cellulose) [13].
An important peak to observe is located at 898 cm-1 where evidences of the C-O-C groups are obseved (related to glycosidic bond β-(1→4)), this groups are the ones that interact with Na+ during functionalization, a reduction in this peak means that the funtional group is establishing a strong interaction with the absorbed Na+ ion [3].
Futher evidences of the presence of Na+ species on the surface of the funtionalized fiber was obtainde by EDS analysis. Figure 2.4 presents the EDS profiles of raw, pretreated and functionalized fibers.
The EDS Spectroscopy for raw and pretreated fibers shows large carbon and oxygen peaks as expected for an organic material and consistent with previous reports [4]. However, the spectrum corresponding to functionalized fique fiber, additionally to the large carbon and oxygen peaks, also shows a strong signal for Na+, related to the ion exchange process that took place when the tretaed fiber was exposed to the cationic agent (NaOH) used in the functionalization process, indicading a suscessfull functionalization process. 2. Physochemical treatment and characterization of Furcraea andina 67
C O Raw Pretreated Functionalized Na Cl
Si Mg Cl Ca
0 0,5 1 1,5 2 2,5 3 3,5 4 keV Figure 2.4. EDS profile of raw, pretreated and functionalized fique fibers 10
The spectrum of Figure 2.4. Evidence of the presence of other elements such as calcium (Ca) and magnesium (Mg) in the raw fiber, which according to Peinado et al.[4], in a characterization previously reported values of 0.96% and 9.4 ppm, respectively. Due to the effect that ultrasound had on the increase of cellulose exposure of some elements that were internally of the fiber such as magnesium (Mg) and calcium (Ca) increasses the intensity, other peaks of elements such as silicon (Si) appeared, which are reported by Peinado et al.[4], like trace values.
Structural characterization
2500 Raw 2000 M30 M60 1500 M90
1000
Intensity a.u.Intensity 500
0 10 13 16 19 22 25 28 31 34 37 40 2 tetha Figure 2.5. XRD of raw and pretreated fiber (30, 60 and 90 minutes of sonication) 11 68 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
2500 M60 2000 MC1 MC2 1500 MC3
1000 Intensity a.u Intensity 500
0 10 13 16 19 22 25 28 31 34 37 40 2 tetha Figure 2.6. XRD of raw and functionalized fiber (1, 2 and 3 hours of functionalization) 12
Figures 2.5 and 2.6 present the XRD profiles for raw, pretreated and functionalized fibers. These results are consistent with cellulose’s diffractograms reporting characteristic broad peaks, the main one centered around 22.6°, which are due to the polycrystalline cellulose character. Peak around 16° is associated with amorphous cellulose (Iam: minimum intensity between the peaks of the planes 200 and 110); while the peak of 22.6° is associated with crystalline cellulose (I200) [29].
The 4 crystalline allomorphs cellulose fique analyzed present the type I (natural and thermodynamically metastable cellulose [37]); this allomorph is a mixture of two different crystal lattices, which change depending on the source of cellulose, plants as fique evidence monoclinic network (Iβ), which has the planes (200), (110) and (110) [30].
Both Figures 2.5 and 2.6 allow to calculate the crystallinity index (CI), which is a quantification of the percentage of crystalline cellulose in the sample; the results are summarized in Table 2.5. Crystallinity index (CI) was calculated using equation (2) as the ratio of the peak heights of I2 0 0 and the minimum intensity of Iam:
퐼푎푚 퐶푖(%) = (1 − ) × 100 퐸푞 (2) 퐼200
Table 2.5. Crystallinity index for raw, pretreated and functionalized fique fiber 15 Raw Pretreated Functionalized IC (%) MC M30 M60 M90 MC1 MC2 MC3 50.30 44.62 49.89 48.49 50.33 36.33 55.11
Table 2.5 shows that the pretreatment effect on cellulose crystalinity is small for any of the pretreatment times of exposure (30, 60 and 90 minutes). Seems like 30 minutes treatment 2. Physochemical treatment and characterization of Furcraea andina 69 is the one that has the major effect, but the crystalinity reduction is only in the order of 6%. In average, the change in crystallinity was only in the order of 2% for the 3 treatments, impliying a sligthly decrease in the amount of amorphous cellulose, which coincides with the results reported by other authors who performed similar pretreatment processes [1, 31, 32].
These result sugested that pretreatments produce no major changes in the cellulose structure, keeping the cellulose steric hindrance to the attack of reagents [29]. However, in Figure 2.6 for the two-hour functionalization time (MC2), a peak shifting at 22° was seen, the interplanar distance of the samples M60, MC1, MC2 and MC3 were calculated using Bragg’s Law, obtaining values of 3.96, 3.95, 3.93 and 3.94Å, respectively. Confirming that the displacement is not related to possible tensions in the crystalline structure of the cellulose.
On the other hand, funtionalization has a major impact on the crystallinity only after 3 hours. since M60 sample was used as starting material for the functionalization process (49.89 of crystallinity index), it is evident that after 1 hour of functionalization there was not effect on the crystallinity of the samples. After 2 hours there was an important reduction to a CI= 36.33 and after 3 hours an increase to CI=55.11. Taking in account that the functionalization process is essentially of chemical nature, exposing the fibers to chemicals such as HCl and NaOH, the CI will be dependent of the reaction rates to which each compound of the fiber interacts with the chemical species of the functionalization chemicals. The crystalline cellulose exposed during the ultrasound treatment is rapidly attack by the surrounded functionalization chemicals and therefore initially there is a reduction on the CI. However upon the time, the chemicals also attack lignin and hemicellulose reducing their amount, exposing more cellulose and improving the crystallinity index [30]. Increasing the amount of crystalline celulose is benificial because this makes the fiber more accesible and susceptible to be used in specific surface chemical reactions [33-36].
As shown in Table 2.5, after 3 hours functionalization process produce the highest percentage of crystallinity index, cause by the realignment of cellulose molecules, this kind of result have also reported elsewhere [37, 38]. 70 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Average crystallite size in the cellulose was calculated from XRD data using Scherrer’s equation [20, 34, 37] (equation (3) ). Based on the line broadening effect at the full width half maximum (FWHM) of the (002) peak. 푘휆 퐷 = 퐸푞 (3) 훽 퐶표푠 휃
Where D is the average crystallite size, k is Scherrer constant, λ is wavelength of X-ray, β is the FWHM and θ is diffraction angle. Results are in Table 2.6.
Table 2.6. Calculated average crystallite size for raw, pretreated and functionalized fique fiber 16 Raw Pretreated Functionalized Average crystal size MC M30 M60 M90 MC1 MC2 MC3 (nm) 11.81 28.2 9.18 5.92 28.21 20.68 5.08
Previous reports have demonstrated for the same peak (002) crystal size in the cellulose calculated by this method, are around 5 to 6, 140 and 5 to 6.2nm, respectively [20, 39, 40], average crystallite size was 28.2, 9.18 and 5.92 nm for 30, 60 and 90 minutes pretreatment, respectively (Table 2.6). The reduction in the crystal size seems to be related to sonication time, accordingly to the fiber degradation mechanism. During the pretreatment, the reduction in the amount of hemicellulose and ligning exposes the cellulose to a stronger effect of sonication, affecting the cellulose structure and size [41], it has been observed that as a function of sonication time the fiber could be more uniform but at the same time the damage in the crystalline cellulose increase [30].
In the functionalization stage, the crystallite size of cellulose decrease to a final size of 5.08 nm, meanly because the chemical treatment remove amorphous material from the fiber [30]. The size of nanoparticles supported on the fiber can be affected by the amount of amorphous cellulose present in the fiber [30], Ciolacu and collaborators reported a similar crystallite size, between 4 to 7 nm, for other natural cellulose material pretreated under similar conditios [29].
Morphological and textural characterization SEM micrographs show the surface of a raw fique fiber covered of scale like structures tidily packed and rectangular in shape, each with an average length of 80 and 25 μm of width (Figure 2.7a). The presence of clusters and aggregates as the observed in Figure 2. Physochemical treatment and characterization of Furcraea andina 71
2.7b and 2.7c are usually associated with wastes from the sheet defibration process. Also some sort of spherical capsules are observed (Figure 2.7d), each with an approximate size of 1μm, which have been tipically attributed to the presence of Streptococcus bacteria [42].
a b
a b
c d
c d
Figure 2.7. SEM micrographs of the raw fiber, a) 250X, b) 500X, c) 2000X, d) 5000X 13
On the other hand, the micrographs of sonicated fibers show that the pretreatment has minor impact on the fique structure (Figure 2.8a), but reduces the roughness of the scales in comparison to the raw fiber (Figure 2.8b), confirming the positive effect of pretreatment. This decrease in the roughness surface is associated with the removal of lignin and hemicellulose. Similarly, it’s clear the elimination of aggregate particles and the presence of bacteria, making the fique fiber pretreated surface much more homogeneous and clean (Figure 2.8c and 2.8d). 72 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
a b
a b
c d
c d
Figure 2.8. SEM of the pretreated fiber M60, a) 100X, b) 500X, c) 1000X, d) 5000X 14
a b
a b
c d
c d
Figure 2.9. SEM of functionalized fiber MC30, a) 100X, b) 300X, c) 1000X, d) 5000X 15
The functionalized fique surface becomes more uniformn and further shows the total elimination of agglomerated particles and the disappearance of scales (Figure 2.9), which confirms that the amount of cellulose exposed increased as a result of the reduction in lignin and hemicellulose after the process of surface functionalization, similar to that reported previously by Chen et al,[15]. 2. Physochemical treatment and characterization of Furcraea andina 73
Table 2.7 present the results for the total surface area inraw, pretreated and functionalized fibers, obtained using the BET method from N2 isotherms. The value of the surface area for the raw fiber is low, as is common in this type of materials, however the treatment seems to have an impact in the development of surface area, probably due the disrruption created in the fiber during the proccess ( for samples M30, M60 and M90), being the M60 the treatment conditions that creates the highest surface area.
The effect of the functionalization process on the surface area is minimal. M60 sample was used as starting material for the functionalization process (3.24 m2/g), it is evident that no major changes in the surface area of the fiber was observed, indenpendly of the time of exposure to the funtionalization process. In Annex 1, the isotherms obtained for the data reported in Table 2.7 are found.
Table 2.7. BET surface area of raw, pretreated and functionalized fibers17 Sample BET surface area (m2/g) Raw 0.77 M30 1.76
M60 3.24 M90 2.48 MC1 3.08 MC2 3.16 MC3 3.18
Thermal characterization All the fiber analyzed by TGA presented an approximate 10% mass loss between 30 to 100°C mainly due to evaporation of moisture present in the fibers (Figure 2.10). After 100oC the raw and pretreated fibers (M30, M60 and M90) follow almost overlapping TGA profiles presenting two major mass loss sections starting at aprox. 260oC (distinguishable by an intermedia inflection around 310oC). This first section has an approximate 18% weight loss related to hemicellulose degradation [41]. The second between 310 and 370°C with an approximate 40% weight loss is generally attributed to cellulose pyrolysis [43] and beyond 370°C almost all cellulose is expected to be pyrolyzed with some remainig material frequently related to lignin. Since lignin decomposition have been reported to happen slowly under a wide range of temperature (from 20 up to 900oC) [41]. 74 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
The functionalized fibers (MC1, MC2 and MC3) also present matching TGA profiles having the same initial water loss showed by the other fibers and also presented almost overlapping TGA profiles between them. However, on the contrary to the behaviour observed for the raw and pretreated samples, the functionalized samples show only one major mass loss starting and ending at aprox. 248 and 348oC. Both, the presence of only one major mass loss and the tempearture shiffting of this mass loss to lower temperature indicates that the functionalization process also modify the structure and composition distribution of the fiber (also observed in the other characterization techniques evaluated), creating a condition in which the hemicelluose degradation process and the cellulose pyrolisis convolute in just one undistinguishable process (at least at the evaluated conditions) [43, 44].
100
90
80
70 Raw 60 M30 50 M60 M90 % Weight % 40 MC1 30 MC2
20 MC3
10
0 30 80 130 180 230 280 330 380 430 480 530 580 T (°C) Figure 2.10. TGA for raw, pretreated and functionalized fiber 16 Conclusions The effect of ultrasound pretreatment and cationization of fique fiber was studied. Beneficial effects on the physicochemical properties of the fiber were found for 60 min of ultrasound pretreatment, increasing cellulose content from 36.33 to 41.42%, while the content of lignin and hemicellulose was reduced from 22.58 to 13.94% and 28.15 to 22.21%. 2. Physochemical treatment and characterization of Furcraea andina 75
XRD confirms that after pretreatment and functionalization there are important amount of crystalline cellulose exposed, after 3 hours of functionalization the CI increased. It was corroborated by EDS and FT-IR analysis, that the functionalization proccess also incorporated Na+ species on the fiber surface, specially the largest impact of the functionalization process was reached after 3 hours of treatment, sugesting the formation of a coordination bond between Na+ ions and the fiber surface carboxylic groups.
SEM pictures showed that both pretreatment and functionalization processes have effect of the surface morphology of the fiber, producing smoother surfaces than the original raw fiber. In terms of the textural properties, the pretreatment has a beneficial impact, increasing the BET surface area. On the contrary, the functionalization process has not impact on the BET area of the fibers. Thermal characterization shows the typical behaviour of lignocellulosic material.
References
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[31] S. Saha, A. Pal, “Microporous assembly of MnO2 nanosheets for malachite green degradation” Sep. Purif. Technol., vol. 134, pp. 26–36, 2014. [32] V. Subramanian, H. Zhu, B. Wei, “Alcohol-assisted room temperature synthesis of different nanostructured manganese oxides and their pseudocapacitance properties in neutral electrolyte” Chem. Phys. Lett., vol. 453, no. 4–6, pp. 242–249, 2008. [33] D. CIolac, V. I. Popa, “Structural changes of cellulose determined by dissolution in aqueous alkali solution” Cellul. Chem. Technol., vol. 39, no. 3–4, pp. 179–188, 2005. [34] E. Doelker “Cellulose in Crystalline Cellulose and Derivatives" Springer Berlin Heidelberg, 2008, pp. 101–174. [35] D. Klemm, B. Philipp, T. Heinze, U. Heinze, W. Wagenknecht, “General Considerations on Structure and Reactivity of Cellulose: Section 2.1–2.1.4” Comprehensive Cellulose Chemistry., 1998, pp. 9–29. [36] K. Kamide, M. Saito, “Cellulose and cellulose derivatives: recent advances in physical chemistry” Biopolymers, Springer, 1987, pp. 1–56. [37] A. Alemdar, M. Sain, “Isolation and characterization of nanofibers from agricultural residues–Wheat straw and soy hulls” Bioresour. Technol., vol. 99, no. 6, pp. 1664– 1671, 2008. [38] G. Li, N. Wang, B. Liu, X. Zhang, “Decolorization of azo dye Orange II by ferrate(VI)– hypochlorite liquid mixture, potassium ferrate (VI) and potassium permanganate” Desalination, vol. 249, no. 3, pp. 936–941, 2009. [39] E. H. Cataño Rueda, “Obtención y caracterización de nanofibras de celulosa a partir de desechos agroindustriales” Repositorio Universidad Nacional de Colombia, 2011. [40] E. Gümüskaya, M. Usta, H. Kirci, “The effects of various pulping conditions on crystalline structure of cellulose in cotton linters” Polym. Degrad. Stab., vol. 81, no. 3, pp. 559–564, 2003. [41] R. Evans, R. H. Newman, U. C. Roick, I. D. Suckling, A. F. A. Wallis, “Changes in Cellulose Crystallinity During Kraft Pulping. Comparison of Infrared, X-ray Diffraction and Solid State NMR Results” Int. J. Biol. Chem. Phys. Technol. Wood, vol. 49, no. 6, pp. 498–504, 2009. [42] K. Ryan, C. G. Ray, N. Ahmad, W. L. Drew, J. Plorde, "Sherris Medical Microbiology" , 5 edition. New York: McGraw-Hill Medical, 2010. [43] K. Raveendran, A. Ganesh, K. C. Khilar, “Pyrolysis characteristics of biomass and biomass components” Fuel., vol. 75, no. 8, pp. 987–998, 1996. [44] J. J. M. Orfao, F. J. A. Antunes, J. L. Figueiredo, “Pyrolysis kinetics of lignocellulosic materials—three independent reactions model” Fue., vol. 78, no. 3, pp. 349–358, 1999.
3. Impregnation of iron compounds on natural and modified fique fiber 79
Chapter 3. Impregnation of iron compounds on natural and modified fique fiber Abstract: A detailed study of the materials synthesized by the impregnation of iron compounds on the surface of natural and modified fique fiber prepared in previous works was performed. Wet impregnation in a contact time range of 1 to 5 days was evaluated in order to assess the amount of iron compounds deposited as a function of time. The amount of adsorbed species was determined by atomic absorption spectroscopy (AAS) and X-ray spectroscopy (XRF). X-ray diffraction (XRD) and Fourier Transformed Infrared spectroscopy (FTIR) were used to determine crystallography, crystallite size and chemical interaction of the iron supported species on the fiber surface. Morphological and textural effects of the impregnation in the fiber were determined via SEM and N2 isotherms. Other properties such as pHzpc, acidic and basic sites and mechanical performance were determined. The obtained results allow to conclude that the chemical functionalization of the fiber plays an important role on the impregnation process, generating high loading density and highly dispersed superficial nanoparticles. XRD and XRF, were used to detect the identity and quantity of elements and compounds that are present in the sample, in this way providing
0 evidence of Fe2O3 (hematite) and α-Fe formation, also revealing that under the impregnating conditions there is not complete evolution of the crystalline structures. No major changes in pHzpc values of the functionalized fiber were observed, neither on the
BET surface areas calculated from N2 isotherms. SEM pictures of the impregnated functionalized fiber revealed areas with substantial aggregation of nanoparticle and areas where they are finely dispersed. Mechanical characterization shows that the impregnated fibers have lower values in the tensile strength and effort to fracture, but higher values for the Young's modulus.
Keywords: Furcraea andina, iron nanoparticles, impregnation, reduction, catalyst. 80 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Introduction Environmental contamination and particularly water pollution is one of the most important global problems as a result of population increase, industrial development and limited resource availability. This context demands solutions involving sustainable criteria, based on the development of processes capable of combining technical efficiency, cost and environmental effect reduction. Leading technologies to address this issues are based on catalytic processes, particularly in the case of water treatment [1].
Currently the most widely used treatments are the combination of physical, chemical and/or biological processes that manage to eliminate or substantially reduce water pollution [2]. Industrial effluents have sometimes certain compounds that make it particularly difficult to remove by conventional treatments, for example azo dyes and heavy metals.
Biological processes are sensitive to toxic and recalcitrant compounds, while other process as adsorption have high costs associated with the management of toxic waste. As an alternative, catalytic processes provide effective treatment alternatives to complex polluted effluents. Their decontamination mechanism are based on the catalytic oxidation/reduction of organic matter employing iron, titanium, copper, manganese or chromium catalysts [3-6].
Current efforts are center into developing new catalysts to make better use of raw materials, reducing at the same time the amount of subproducts. Authors such as Corma et al.[7], Ramirez et al.[8], and Chacon et al. [5], have developed catalysts based on bogsita (zeolite), saponite (clay) and a biocomposite (nanostructured MnO2 and fique fibers), respectively, catalysts with applications in wastewater remediation.
Additionally, nanotechnology has provided novel and efficient solutions to environmental problems, specifically iron nanoparticles have demonstrated exceptional adsorption and catalytic properties, due to fact that iron species are easily oxidized by organometallic pollutants, amines and phenols [9].
In previous works, a cellulose matrix obtained from fique fiber was physical and chemically modified as a means to provide enhanced characteristics as a catalytic support; in order to take advantage of these enhanced properties a suitable procedure of loading the catalytic active phase (iron compounds, in this particular case) must be developed. Supported 3. Impregnation of iron compounds on natural and modified fique fiber 81 catalysts can be synthesized by different techniques depending on the characteristics of the support material and the active phase to be supported. Procedures such as precipitation and co-precipitation, are very useful in cases in which the active phase is formed by precipitation from a precursor salt in solution. Co-precipitation is used in those cases in which the active phase of the catalyst is composed of more than one component, so that simultaneous precipitation occurs [10].
Impregnation is a technique used to produce supported catalysts that involves the intimate contact of the solid support with a liquid containing the active elements (impregnating solution) of the future catalyst; the amount of impregnating solution used may be slightly in excess to the amount necessary to cover the support and is denominate wet impregnation [11, 12]. Wet impregnation has greater application in cases in which chemical interaction between the support and the impregnating solution are expected [10]. Impregnation is not an exclusive mechanism, ie, other parallel processes can occur such as competitive adsorption or selective deposition and ion exchange, among others [12]. Both chemical adsorption and ion exchange, are mechanisms that involve chemical interaction at the surface level of the active phase and the support, generally by covalent type functional groups [13]. In particular, the anionic exchange allows to controllably impregnate a metal from an aqueous solution on a catalyst support functionalized surface. Catalysts prepared by impregnation are characterized by high activity, homogeneous shape, size and dispersion, due to depending the precursor/reducing agent relation.
Materials and methods:
Catalyst Preparation Raw, pretreated (M60) and functionalized (MC3) fique fiber were used as support for the aqueous impregnation of iron species. A solution of Iron chloride (Merck, Darmstadt, Germany) and deionized water (0.45 μS/cm, Milli-Q®), were used to prepare the impregnation solutions. In situ synthesis was performed using FeCl3 as precursor, being a precursor that doesn’t require heat treatment in the process of synthesis, then it doesn’t affect the physicochemical properties of the support. Likewise, it is an economic precursor and extremely soluble in water, allowing the Fe+3 ions to interact with the electrostatic character of the support, increasing the number of anchored species [17]. 82 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
The support was submerged in 50mL of a FeCl3 58mM solution varying the impregnation time for 1, 2, 3, 4 and 5 days. Samples of the impregnated material were taken at the end of each day, removed from the impregnating solution and washed three times with deionized water to remove loosely bound particles and leftover species from the functionalization and impregnation process[14]. Then, the wet impregnated fibers were immersed in a 1M NaBH4 solution (Merck Millipore®) during 10 minutes to provide +3 reductive conditions, keeping the molar ratio 2:1 (BH4ˉ / Fe ) [15]. According to the following reaction:
0 2퐹푒퐶푙3 + 6푁푎퐵퐻4 + 18퐻2푂 → 2퐹푒 + 6푁푎퐶푙 + 6퐵(푂퐻)3 + 21퐻2 Eq (1)
Then the reduced fibers were rinsed with abundant deionized water. Finally, the catalyst was dried at room temperature overnight [16]. It is important to highlight that even up to the fourth day of impregnation there was enough impregnating solution to cover the whole support material.
The mechanism of formation in solutions by reducing Fe+3 ions is performed in two stages: nucleation and growth. Nucleation represents the first stage during a crystallization process, it can be defined as the process by which building blocks (metallic atoms in the synthesis of metal nanomaterials) arrange themselves according to their crystalline structure to form a site upon which additional building blocks can deposit over and undergo subsequent growth. Properties of nanoparticles as size and shape are function of the reaction rate, which at the same time is controlled by parameters such as concentration, temperature, pHzpc, pH, reductive power, solubility and nature of metal ion [18,20]. A general mechanism of iron nanoparticle formation is shown in Figure 3.1 [19].
Figure 3.1. Mechanism of formation of iron nanoparticles [19] 17 3. Impregnation of iron compounds on natural and modified fique fiber 83
Characterization The iron content of the catalysts after impregnation was determine by means of flame atomic absorption spectrometry (FAAS) using the injection method. Before the performing the atomic absorption the samples underwent a digestion procedure following the EPA Method 3050B: Acid Digestion of Sediments, Sludge, and Soil [21]. Then, the material obtained from the digestion procedure was analyzed in a Hitachi z-8000 atomic absorption spectrometer equipped with an atomizer with air/acetylene burner used for the determination of elemental iron. The wavelength used for the determination of the analyte was: Fe 248.3nm. The content of iron and other element was also followed by X-ray fluorescence spectroscopy (XRF), on pressed 36 mm in diameter tablets molded on a hydraulic press at 120 kN per minute, using a MagixPro PW – 2440 Philips spectrometer equipped with a tube Rhodium and maximum power of 4kW. The semiquantitative analysis was performed with the IQ software, after 11 sweeps of X-ray fluorescence. pH of zero point charge (pHzpc) was estimated using the pH drift method [22]. For this purpose, 50 mL solutions of KNO3 (1% vol.) were adjusted to initial pH values between 2 and 10 with solutions of NaOH 0.1M or HCl 0.1M. Then, 0.1g of catalyst was added into this solution, after 24 hours the final pH of the solution was determinate. Acid and basic sites of the fibers were determined using Boehm titration method [23], the titrants solutions were 0.1 M NaOH or HCl according to the case, the data were reported as meq of titration solution/g.
An XPERT-PRO MPD diffractometer with monochromator of graphite crystal was used to characterize the crystalline structure of the materials. Cu Kα radiation at wavelength of 1.54Å were used as X-rays source and were recorded over 2 theta range of 5º– 85º. Experimental data was analyzed using PANalytical X'Pert HighScore Plus database. Crystalline size of identified structures was calculated using Scherrer equation.
Morphological characterization was performed using a Zeiss Neon 40 Scanning Electronmicroscope (SEM) operating between 2 to 20kV, functioning at an average 5 mm working distance, on previously thin film Pt coated samples (1 to 3nm thick). Total surface area was measured by the adsorption of nitrogen (N2) at 77K, using a Quantachrome
NOVA e-Series surface area analyzer. N2 isotherms were performed on samples degased at 80oC for 8 hr; the calculation of the total superficial area was done using the BET method [23]. 84 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Infrared spectra of the catalyst were collected on a FT-IR spectrometer (Nicolete iS 10 (Thermo Fisher Scientific)) in the range of 400 to 4000cm-1 with a resolution of 4cm-1, using a diamond crystal ATR (PIKE) accessory.
DLS experiments were done in a Malvern Zetasizer Nano Range equipment using 1000μL of the lixiviated solution of nanoparticles; measurements were taken by triplicate at 25°C, 54.2kcps count rate and for 50s of scanning time. The mechanical performance of the materials was determinate using a tensile testing machine (Shimadzu AG-IS) with a 50N cell load. Experiments were performed with a cross head speed of 3mm/min at room temperature (18°C) and a relative humidity of 54.6%. The results were averaged over six measurements, the statistical analysis of the data each sample excludes outliers, employing software Matlab®.
Results and discussion
Impregnation process The initial observation surveyed during the impregnation process, regardless of effect of the impregnation time, was a dramatic change of the fiber color from yellow (Figure 3.2a) to coppery brown (Figure 3.2b), this change in coloration have been frequently related to the chemical state and particle size of the impregnated particles. In the particular case of nanoparticles, some authors have shown that nanoparticles in solution [20,21,24] and anchored to supports such as cotton fibers and cellulose [5,14] show color variations due to changes in the properties of the surface plasmon resonance of the material [22,23].
a b
a b
Figure 3.2. Color change on impregnated fibers. a) Before impregnation (functionalized stage) b) After impregnation 18 3. Impregnation of iron compounds on natural and modified fique fiber 85
Although the change of the fiber color was a primary indication of the effect of the impregnation process on the surface, it was necessary to corroborate the amount and chemical condition of the impregnated species on the fiber surface. Consequently the amount of Fe species supported after impregnation on the raw, pretreated and functionalized fique fiber was measured using FAAS following the procedure describe in the experimental section and the results are presented in Figure 3.3.
Independently of the initial stage of the fiber before the impregnation (raw, pretreated or functionalized) the three materials presented a fast increase in the amount of Fe supported in the first day of impregnation, after the first day, all the materials presented a tendency of stabilization of the amount of iron species supported.
Although, this behavior is shared for the three materials, there is an important difference between the net amount of Fe species supported, meanwhile the raw and pretreated sample at the end of the first day have a Fe species loading of 5.5wt %, the functionalized fiber reached a value in the order of 10.9% after 1 day of impregnation, implying that the functionalization treatment has an beneficial effect on the impregnation of Fe species on the fiber surface. After 5 days of impregnation the final Fe species loading values obtained were 6.6, 11.7 and 14.9wt% for the raw, pretreated and functionalized fibers, respectively.
18%
16%
14%
12%
10%
8%
6%
4% Fe impregnated (wt.%) impregnatedFe 2% Raw Preteated Catalyst
0% 0 1 2 3 4 5 Impregnation (Days) Figure 3.3. Amount of Fe species impregnated on raw, pretreated and functionalized fiber as a function of impregnation days 19 86 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
The results observed in Figure 3.3 determined by FAAS, highlighted the importance of the functionalization process and the proper chemical configuration of the fiber surface to interact with the ions contained in the impregnation solution; the initial raw fiber is schematically presented in Figure 3.4a, once the fiber is cationized during the functionalization process, positive charged Na+ species populate the fiber surface (Figure 3.4b), these Na+ ions interact with Fe species in the precursor solution leading to the deposition of Fe+3 ions on the fiber surface via ion exchange, generating NaCl in solution; a final reduction step with NaBH4 (reducing agent) is implemented with the aim of maintaining the reduced state of the Fe species at least during the deposition of the Fe on the fiber surface, although this reduction step does ensure the final oxidation state of the impregnated species due to the fact that this final reduction state of the iron aggregates particles is also depending of their interaction with the surface, environmental conditions, among others [29].
Figure 3.4. Chemical synthesis of nanoparticles by the impregnation method (Adapted from [5]) 20
XRF was also used to verify the amount of iron species impregnated on raw and functionalized fiber after the first day of impregnation, expresses as oxide. The results presented in Table 3.1, confirms an important increment in the Fe related compounds (due to the impregnation); some Na and Cl related compounds are also present, which are leftover from the acid digestion (HCl) and the subsequent cationization (NaOH) stages of the functionalization process. Other compounds of Si, S and Al are present in the natural fiber and had small changes in the composition of the fiber before and after impregnation.
The functionalization of fique fiber has an appreciable effect on iron deposition as a result of chemical bond formation between the iron nanoparticles and the sodic active groups 3. Impregnation of iron compounds on natural and modified fique fiber 87 attached to the surface during the functionalization. In the case of the raw and pretreated fiber, impregnated iron is lightly attached to the fiber surface as a consequence of weak interactions (mainly Van der Waals type forces). However, comparing the amount of final iron presented in the pretreated and raw fiber, is it clear that the ultrasound pretreatment also have some and effect on the capability of the fiber to support iron, predominantly due to the cellulose exposing effect that the ultrasound treatment has on the fibers, which is also reflected in the increase of surface area observed in the fiber after the treatment; besides the observed increment in the surface area this type of ultrasound pretreatment has been also reported to increase the number of hydroxyl groups available for further functionalization or chemical interaction to absorbing species [30].
Table 3.1. XRF analysis of raw fique fiber and catalyst with 1 day of impregnation 18 Element and/or Raw fiber 1 day of compound (wt%) impregnation (wt%)
Fe2O3 0.097 7.033
Na2O 0.022 2.919 Cl 0.027 0.279
SiO2 0.100 0.133
Al2O3 0.012 0.031
On the other hand, on the surface of the functionalized fiber the process of deposition is
- + mainly driven by an electrostatic environment created by the –CH2O Na groups formed on the surface during the functionalization process, the interaction of this group via ion exchanges creates a strong anchoring effect on the impregnated nanoparticles and the surface fiber through chemical bonds, the attractive forces of this mechanisms have been described to be normal to the surface of the support [16,31]. This chemisorption process creates real irreversible chemical bonds that do not occur homogeneously throughout the support, but only in some active sites [32]. Also, chemical interactions take advantage of oxygenated groups (such as hydroxyl and ether) typical of cellulosic surfaces, allowing the anchoring of ferric ion to the cellulose fibers by ion-dipole interactions that stabilized the nanoparticles, producing high dispersion of the active phase and assisting the formation of iron nanoparticles on the surface of the support. It would be foreseeable that on the initial days there is concurrent contribution of the chemical driven and of the physical driven impregnation mechanisms, however as the amount of surface chemical active site available is limited, it is expected that is contribution will decay upon time. 88 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
During the second day of impregnation on the functionalized fiber there was an increment in the percentage of iron impregnated, this increment could be the result of the interaction of the remaining available –CH2O-Na+ groups on the surface that did not readily interacted with the Fe+3 in the impregnating solution. The physisorption mechanism has a contribution on the amount of Fe+3 impregnated on the fiber or even on top of already impregnated Fe+3, leading to the formation of "clusters" or new larger aggregations on the fiber surface [5,33].
After the second day, it seems that the impregnation process is reaching an equilibrium stage and on the subsequent days the amount of deposited iron did not significantly change. As the available chemical active sites of functionalized fiber being covered by impregnated species decrease as function of time meanwhile the physical impregnation could be still happening in the available uncovered surface area or even on top of already impregnated species (creating bigger particles or aggregates), it is expected that most of the particles adsorbed during the final days are only physisorbed and therefore weakly absorbed when compared to the chemisorbed ones [16]. A secondary effect of the aggregation of particles is the reduction of the effective surface area of the particles available for reaction [15] and generating saturation of Fe+3 ions in the active sites on the surface of fique that can leach later on.
Few literature is available on the deposition of iron compounds on fique fiber, however comparable procedures of the impregnation of MnCl2 solutions have been reported by Chacón et al. [5], they reported a final amount of manganese impregnated compounds in the order of 1 and 1.84wt %, lower than the final amount obtained for the present study. 3. Impregnation of iron compounds on natural and modified fique fiber 89
Day 1 Day 2
Day 3 Intensity a.u.Intensity
5 8 11 14 17 20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 65 68 71 74 77 80 83 2 tetha Figure 3.5. XRD diffractogram profiles of functionalized fiber after 1, 2 and 3 days of impregnation.21
In order to establish the reduction/oxidation state of the formed particles after impregnation, XRD profiles of selected samples were obtained. Figure 3.5 shows the evolution on the crystallization and chemical species of the impregnated material during the three initial days of impregnation for the functionalized fiber, there are not significant differences in the profile observed, all of them clearly show cellulosic related peaks (located at 2theta of 16 and 22o), a small broad peak centered around 34° related to the o Fe2O3 structure (specifically corresponding to hematite) and a tiny peak around 81.2 which coincides with the secondary (211) plane of α-Fe0, however the main (100) peak of the α-Fe0 structures is not observed at 44.67o [34]. The size and the shape of the iron related peaks on the XRD profiles does not have major changes from day 1 to day 3, supporting the observation that the main impregnation process probably happens in the initial days of impregnation. An additional information that can be extracted from the XRD profile is the crystal size using the Scherrer equation, due to the presence of broad peak
(characteristic of nanoparticles); the average size calculate for the Fe2O3 34° peak was 28.2nm.
The fact that only the main peak of hematite (lacking some secondary peaks) and that only a secondary peak for the α-Fe0 are observed indicates that under the impregnating conditions there is not a complete evolution of the crystalline structures. It is well established that a complete crystallization of the γ -Fe2O3 (maghemite) and the α-Fe2O3 (hematite) phases occurs at temperatures around 300 and 350°C, respectively. The 90 Wastewater treatment using an iron nanocatalyst supported on Fique fibers transition from the maghemite to the hematite occurs at 500°C [33-35]. In the context of this study a post treatment of the impregnated fibers was not considerate due to the low temperatures in which the natural fiber materials start to degrade.
Some studies [34-36] have reported that supported amorphous iron oxides nanoparticles could be stabilize due to interaction with the matrix in which are supported, in concordance with the lack of proper crystallinity development observed in the in this study. The lack of crystallinity in iron nanoparticles (α-Fe2O3 or γ-Fe2O3) structures have been also explained by fact that at such small dimensions, space restrictions entail to the absence of a periodic network could arise [35].
The results obtained by XRD, atomic absorption and XRF confirms the presence of iron on the support´s surface and the effects of the impregnation time spam in the amount and chemical state of the particles impregnated. Although, the values of the percentages obtained by atomic absorption and XRF are not one to one quantitatively comparable due to intrinsic characteristics of the techniques (XRF is a semiquantitative technique of characterization doesn’t include the analysis of Al lighter elements), the techniques are complementary and give a more complete picture of the phenomena.
Further evidence on the chemical interaction of the impregnated Fe species and the functional groups on the surface of the functionalized fiber was obtained by FT-IR; Figure 3.6 shows the FT-IR spectra of the impregnated functionalized fiber for the 1, 2 and 3 days of impregnation; these have the characteristic strong absorption bands between 450 to 600cm-1 related to the presence of iron oxide related compounds [35]. Specifically for γ-
-1 Fe2O3 (maghemite) two peaks around 463 and 1630cm were identified, the first one may correspond to Fe-O bending vibration mode. A broad peak at 162cm-1 and two peaks in
-1 463 and 546cm were observed, which are the characteristic absorption bands of α-Fe2O3 (hematite) [36], it is important to note that the peak at 463cm-1 doesn’t allow to distinguish between maghemite and hematite phases. Likewise, two stretching vibrations at 420 and 618cm-1 were observed, these are characteristic of Fe-O interactions bringing evidences of 0 the existence of zero valent iron supported species, providing additional support to the Fe diffraction peak observed in the XRD profiles [37]. 3. Impregnation of iron compounds on natural and modified fique fiber 91
Transmittance % (u.a) % Transmittance
3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm-1) Day 1 Day 2 Day 3 Functionalizated MC3 Figure 3.6. FTIR spectrum of functionalized fiber after three different days of impregnation (1, 2 and 3 days) and without impregnation 22
The vibration located at 898cm-1 is related to the insertion of Na+ ions on the carboxylic groups of the fiber surface and are still observed on the functionalized fiber [33]. Also evidences of the presence of oxyhydroxide [FeO (OH)] can be observed at 1100 cm −1 [35].
Due the important role the ion exchange process has in the mechanisms of Fe species impregnation on the surface of the fiber and its possible effect in the modification of the charge distribution on the fiber surface, pHzpc values were also determinate for the impregnated material on the functionalized fiber, these results are reported in Table 3.2. No major change in the pHzpc values were observed during the three days of impregnation, maintaining values between 8.56 to 8.83 (average 8.71 ± 0.08), suggesting a slightly basic character when compared to the original pHzpc value of the functionalized fiber before exposed to the impregnation solution (pHzpc = 8.23 ± 0.08). This slight change is related to specific properties that the iron oxide nanoparticles formed during the impregnation process have been reported to display, regarding to their ability to change valence to form complexes with many organic and inorganic compounds and to have an amphoteric character when interacting to H+ and OH- ions species, as the ones present in the precursor solution [33]. The presence of iron oxide (Fe2O3) in the forms of γ-Fe2O3
(maghemite) and α-Fe2O3 (hematite) on the surface of the impregnated functionalized fiber explains the predominant alkaline surface. Also contributing to this alkalinity are [FeO(OH)] groups, some reactive hydroxyls groups on the cellulose and possibly some remaining Na+ ions. 92 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 3.2. Acidic and basic sites determined by titration Boehm and pHzpc for the impregnated functionalized fiber 19 Impregnation Acidic sites Basic sites pHzpc days (meq/g) (meq/g) 1 0.100 ± 0.035 0.763 ± 0.053 8.73 ± 0.06 2 0.375 ± 0.071 0.825 ± 0.035 8.84 ± 0.16 3 0.200 ± 0.035 0.750 ± 0.071 8.56 ± 0.02 pHzpc values also may help to explain the differences in the amount of Fe impregnated observed for the raw and pretreated fibers when compared with the functionalized fiber; as the adsorption mechanism involved in the impregnation of the raw and pretreated sample is essentially due to physisorption, the acidic condition of the impregnating solution (pH =
1.96 ± 0.14) affect the charge distribution on the raw and pretreated fiber surfaces (pHzpc of 5.39 and 4.18, respectively), creating the conditions to have fiber surfaces positive charged, hindering the ability of the impregnating Fe+3 cations to interact with the surface [38].
Table 3.3. BET surface area of functionalized fiber after impregnation 20 Impregnation days BET surface area (m2/g) 1 3.12
2 3.08 3 3.21
Surface area of the impregnated functionalized fiber was obtained from N2 isotherms data and calculated using the BET equation, the result are reported in Table 3.3. It could be concluded that for the functionalized fiber the impregnation process has little or none effect on the surface area. The BET area of the functionalized fiber before the impregnation process was 3.18 m2/g and after the impregnation oscillates between 3.08 to 3.21m2/g. Significant changes, particularly reduction, on surface area supported materials due to impregnation process is usually the effect of pore mouths blockage by impregnated particles, obstructing the diffusion and further adsorption of N2 molecules during the isotherm determination (and effectively, any other molecule that tries to diffuse into the pore); the effect of pore blockage is neglectable on low surface area materials, as the functionalized fiber. In Annex 2, the isotherms obtained for the discussed samples are reported in Table 3.3. 3. Impregnation of iron compounds on natural and modified fique fiber 93
Figure 3.7. Morphological analysis of the functionalized fiber surface after 1 day of impregnation a) SEM 5000X, b) SEM 5000X, c) backscattering 30000X, d) backscattering 30000X 23
Morphological characterization of the impregnated material can be observed in the SEM pictures shown in Figure 3.7. Figure 3.7a and 3.7b correspond to low magnification SEM pictures of the functionalized fiber surface after 1 day of impregnation, this pictures seems to indicate that the fiber surface is unevenly covered by impregnated nanoparticles, some areas look denser populated by micron size cluster of nanoparticles meanwhile others seems to look uncovered (Figure 3.7a and 3.7b); however, at higher magnification (Figure 3.7c) it is possible to observed that the surface is covered by two types of nanoparticles, some of them are clearly conforming large aggregates of clustered nanoparticles (red line enclosed area) and some others are finely dispersed nanoparticles (blue line enclosed area). Backscattering analysis was performed on the surface of the fiber corresponding to the Figure 3.7c and the results are presented in Figure 3.7d, confirming that both the aggregates and the fine particles are iron compounds, this backscattering analysis allows to do an estimation of particle size of the nanoparticles, some of them are in the range of 100 to 200nm, especially the ones conforming the aggregates, on the contrary the one that seem to be finely dispersed have particle size below 100nm, some of them even below 50nm. 94 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Figure 3.8. SEM pictures of the functionalized fiber surface after 2 days of impregnation a) 3000X, b) 10000X, c) 35000X, d) 70000X 24 25
Figure 3.8 shows the SEM pictures of the functionalized fiber surface after 2 days of impregnation. Figures 3.8a and 3.8b correspond to low magnification SEM pictures where the fiber surface seems to be more densely covered, which may be a reflection of the higher Fe wt% determinate by atomic absorption for the second day of impregnation when compare to the value obtained for the first day. Figure 8b also shows some aggregation of particles that are loosely attached to the surface, almost peeling off from it. Figures 3.8c and 3.8d are high magnification pictures of the aggregates that confirms that those aggregates are clusters made out of smaller particles, most of them in the order of 100nm or smaller.
The aggregates loosely attached to the surface would be the result of the particles impregnated mainly by physical forces and will be prone to uncouple from the surface. In order to evaluate the capability of the particles to stay attached to the surface a lixiviation experiment was performed simulating the reaction conditions in which the catalyst would be evaluate, the resulting lixiviated solution was analyzed by atomic absorption and 3. Impregnation of iron compounds on natural and modified fique fiber 95 dynamic light scattering (DLS) in order to establish the amount and size of the lixiviated particles.
Figure 3.9. Size distribution leached of iron nanoparticles (1day of impregnation) in aqueous solution (Malvern Zetasizer Software)26
Figure 3.9 shows the particle size distribution for the three runs, all of them presented a broad normal distributed peak ranging from around 50 up to around 500nm, with a polydispersion index (PDI) 0.408 and an average particle size of 147nm. Some of the particles size distribution plots showed an extra small peak at higher particle size (around 8 microns), probably coming from the big loosely aggregates observed on Figure 3.7b. Atomic absorption results indicates that only 5.38% of the impregnated Fe lixiviated from the fiber surface, meaning that the impregnated particles are strongly attached to fiber surface.
Mechanical characterization
Maximum force and maximum displacement were measured, while maximum stress and maximum strain were determine for the raw fiber, pretreated and functionalized fibers (1, 2 and 3 days of impregnation). A summary of the obtained data is presented in Table 3.4, where the fique density value (0.72g /cm3) used for calculations of cross sectional area was taken from Amoy et al. [39]. 96 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 3.4. Summary of mechanical characterization for raw and impregnated fiber (1, 2 and 3 days) 21 Cross Maximum Stress strain Young’s Strain to Sample sectional force (N) (MPa) Modulus (MPa) failure (%) area (mm2) Raw 0.036±0.015 7.586 ± 3.828 177.18±73.01 3267.40 ± 838.86 8.57 ± 3.20 Day 1 0.052± .024 3.761 ± 1.240 90.76 ± 49.07 924.61 ± 446.08 10.97± 2.99 Day 2 0.054± .016 4.192 ± 0.984 77.86 ± 10.79 2775.00 ± 463.09 5.27 ± 2.07 Day 3 0.083± .057 5.237 ± 1.870 71.40 ± 29.09 4518.9 ± 1322.67 6.25 ± 2.99
Based on the maximum force (F max) and cross sectional area (N) was determined for each fiber using the equation (2):
퐹 푚푎푥 (푁) 휎 (푀푃푎) = 퐸푞 (2) 퐴 (푚푚2)
Test Shapiro-Wilk was applied, confirming the normality of the data, in terms of variance homogeneity data series was found that the data series is homoscedastic through Levene test. Statistically through an analysis of ANOVA there is no evidence that the more days soaking decrease the stress - strain of the impregnated samples with iron nanoparticles, but evidence was found that all catalysts generally have less stress – strain in relation with the raw fiber (see Table 3.4); strain was calculated from the equation (3).
∆푙 (푚푚) 휀 = (3) 퐿표 (푚푚)
Using the stress-strain slope in the initial elastic regimen (between 10% to 30% shown in Figure 3.10), the elastic modulus (E) was calculated for each tensile tested fique fiber.
Concerning the influence of surface treatments on the stress properties of natural fibers, was possible to appreciate a reduction in the maximum strength and the deformation capacity of the catalysts regarding raw fiber (Figure 3.10), while the elastic modulus increased.
This mechanical behavior catalysts, not only is attributed to the presence of nanoparticles but also the chemical and physical treatments explained in Chapter 2, which generate an apparent stiffening of the fiber, as a result of changes in the bionanocomposite structural chemistry (percentage of lignin, hemicellulose and cellulose) [40].
3. Impregnation of iron compounds on natural and modified fique fiber 97
Figure 3.10. Curves stress vs strain of a) raw fiber b) catalyst with 1 day of impregnation c) catalyst with 2 day of impregnation d) catalyst with 3 day of impregnation 27
The crystal lattice of the matrix in this case cellulose, strongly influences the overall mechanical properties affecting the reduction in the stress strain as a consequence to the cationization stage in the surface functionalization. Altering the orientation of the cellulose chains which in turn defines the structure of the crystals and the crystallinity percent, resulting in a change in the crystalline structure of cellulose I type II to type [41]. In addition, the effect of bonding strength of each iron nanoparticles also influences the reduction in this property.
As for the reduction in the percentage of strain to failure (deformation) is associated with the presence of defects in the fiber, caused by low interfacial properties between iron nanoparticles or nanoparticle-support, own properties of the support and nanoparticles, morphology, size and low crystallinity of the nanoparticles. Increasing the likelihood of finding these irregularities in the filaments, and thus the generation of inferior mechanical properties [42].
In the other hand, the increased elastic modulus may be related to intra and intermolecular bonds of H2, generated because crystal size bulk aligned in parallel along the axis of the fibrils. Causing the number of fibrils of cellulose significantly influences the properties of 98 Wastewater treatment using an iron nanocatalyst supported on Fique fibers the resulting compounds, in other words, amongst finer the structure as nanocellulose is Young's modulus and greater stiffness [40].
It is important to clarify that the standard deviations obtained for maximum strength, the elastic modulus and percent strain at maximum load, are allocated to the area of the cross section and geometry varies along fique filaments, conditioning the mechanical dispersion of the material results. This heterogeneity of natural fibers constitutes one of the drawbacks when employed as reinforcement in composite materials [42].
Conclusions A study of the materials synthesized by the impregnation of iron from aqueous solutions on the surface of natural and modified fique fiber was performed. Initially it was observed that the impregnation process is influenced by the condition of the fique fiber; raw, pretreated and functionalized fiber presented a fast increase in the amount of Fe supported in the first day of impregnation followed by a stabilization tendency of the amount of Fe supported in the following days of impregnation (up to 5 days). However, the net amount of impregnated Fe differs depending of the fiber condition being the functionalized fiber the one with the higher amount of impregnated Fe all along the impregnation process, the final amount of Fe impregnated was 6.2, 11.1 and 14.9 wt % for the raw, pretreated and functionalized fibers, respectively. This results highlighted the importance of the functionalization process and the proper chemical configuration of the fiber surface in the impregnation process. FT-IR confirmed the presence of Na+ on the functionalized fiber surface promoting the chemical bonded adsorption of Fe species. Meanwhile on the functionalized fiber the chemically driven adsorption has an important role, the physical driven adsorption is the dominant one in the raw and pretreated fibers
XRD profiles of the functionalized fiber after the impregnation process allowed to conclude
0 that iron species supported on the fiber surface correspond to Fe2O3 (hematite) and α-Fe . The size and the shape of the iron hematite peak indicates that these are essentially iron nanoparticles (28.2nm calculated using the Scherrer equation). The fact that only the main peak of hematite (lacking some secondary peaks) and that only a secondary peak for the α-Fe0 are observed indicates that under the impregnating conditions there is not a complete evolution of the crystalline structures. 3. Impregnation of iron compounds on natural and modified fique fiber 99
Further evidence on the chemical interaction of the impregnated Fe specie and the functional groups on the surface of the functionalized fiber was obtained by FT-IR where the characteristic stretching vibrations between 450 to 600cm-1 revealed the presence of iron oxide compounds. Specifically for γ-Fe2O3 (maghemite) two peaks around 463 and 1630cm-1 were identified, the first one corresponds to Fe-O bending vibration mode. A broad peak at 162 cm-1 and two peaks in 463 and 546cm-1 were observed, which are the characteristic absorption bands of α-Fe2O3 (hematite). Two additional stretching vibrations at 420 and 618cm-1 revealed the presence of Fe-O interactions confirming the existence of zero valent iron supported species observed in the XRD profiles [31].
No major change in the pHzpc values of the functionalized fiber was observed during the three days of impregnation, maintaining values between 8.56 to 8.83 (average 8.71 ± 0.08), suggesting a slightly basic character when compared to the original pHzpc value of the functionalized fiber before exposed to the impregnation solution (pHzpc = 8.23 ± 0.08). In terms, of the raw and pretreated fibers the acidic condition of the impregnating solution creates positive charged surface hindering the ability of the impregnating Fe+3 cations and explaining the differences in the amount of Fe impregnated observed for the raw and pretreated fibers when compared with the functionalized fiber.
BET area of the functionalized fiber is not affected by the impregnation process mainly due to initial low surface are of the sample (characteristic of materials lacking meso and microporosity) prevents any surface area loss due to pore mouth blockage.
SEM pictures of the impregnated functionalized fiber after 1 and 2 days showed that the fiber surface is unevenly covered by impregnated nanoparticles, high magnification SEM pictures allow to verify that densely populated area correspond to finely dispersed nanoparticles, this conclusion was confirmed via backscattering analysis. SEM pictures of the 2 days impregnated functionalized fiber shows some aggregation of particles that are loosely attached to the surface; lixiviation experiments were performed showed that the amount of lixiviated particles is minor (only 5.38% of the impregnated iron) and the particle size distribution of these particles present a broad normal distributed peak ranging from around 50 up to around 500 nm, with an average particle size of 147 nm. Some of the particles size distribution plots showed an extra small peak at higher particle size (around 8 microns), probably coming from the big loosely aggregates. 100 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Mechanically the impregnated fibers were shown to have lower values in the tensile strength and effort to fracture, but higher values for the Young's moduli, which could be a reflection of the interactions between the fiber matrix and the nanoparticles, as well as characteristics of each of the constituent elements of the impregnated material.
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104 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Chapter 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalysts Abstract: Degradation and mineralization of the dye Orange II (OII) was performed with nanoparticles supported on fique as catalysts in reactions conditions that promotes the heterogeneous Fenton reaction. A Box-Behnken experimental design was used to −5 −4 evaluate the effect of: pH (2.5 - 3.5), initial OII concentration: 퐶푂퐼퐼0 (2푥10 - 2푥10 M), initial hydrogen peroxide concentration 퐶 (1푥10−4 - 10푥10−3M) and load of iron in the 퐻2푂20 catalyst (10.9, 14.9 푎푛푑 13.2) wt.% in the degradation of OII. A 93.23% of degradation was obtained after 4 hours of catalytic activity under following conditions: pH: 2.5, 퐶푂퐼퐼0: 1.1푥10−4푀, 퐶 : 5.05푥10−3M and 10.9 퐹푒 %푤푡. pH was determinate to be the most 퐻2푂20 influential variable in the degradation process, reporting to have better degradation at lower pH. A simplified pseudo-first-order kinetic model was proposed and described 16 of the degradation conditions with a R2 above 0.9; a very remarkable result for such a simple model. Catalyst deactivation was tested for 7 consecutive cycles, showing that the catalysts kept high activity up to 4 cycles. The effect of Cl- ion in the OII degradation was determinate to be damaging in term of degradation rates for concentration as low as 0.05M and damaging both, degradation rate and final degradation value for 0.1 M.
Keywords: Fenton, water treatment, Orange II, fique, iron nanoparticles.
Introduction Recalcitrant compounds are chemically resistant to degradation, reason why it is an important topic of current research to find a process that safely convert these contaminant 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 105 compounds into components with the higher stable oxidation state through a mineralization process. Industrial activities generate high percentages of wastewater, which in some cases are directly discharged into effluents, affecting the environment [1].
Azo dyes, extensively use in industry, are potentially carcinogenic and toxic because aromatic amines are present in their chemical structure. OII (C16H12N2NaO4S), is a heterociclyc anionic azo compound from the group of naphthols, use as dye in the textile, cosmetic, silk and paper industries [9]. Additionally, OII is a non-biodegradable compound that poses a potential risk to human health [7,8].
Treatment of effluents contaminated with dyes used physical, chemical and biological processes and frequently they are not completely effective [6], as only they change the pollutant from one stream to another (physical processes) or may have very slow degradation rates (biological processes) [7]. In addition, currently there are alternatives such as activated charcoal [8], ozone [9] and hypochlorite [4], but are inefficient alternatives for secondary waste generated (residual chlorine) and costly in terms of operation, equipment and production.
Advanced oxidation processes (AOPs) has been proposed as an alternative solution; AOPs used oxidation Fenton's reagent to degrade and mineralize effluents contaminated with dyes, it is a particular case of wet oxidation with hydrogen peroxide (CWHPO) and has the advantage of being efficient even at ambient temperature and pressure, it is a also a simple and economic process [10].
The reaction between iron and hydrogen peroxide (an important mechanism in the Fenton oxidation process), increases the amount and reactivity of hydroxyl radicals produced in acid solution by peroxide decomposition, these species attack the organic matter present in the reaction medium, due to oxidative power that the radicals generated on the surface of the solid [11]. The effectiveness of the catalyst in the oxidation of dyes is influenced by the synthesis variables (explained in previous works) and the reaction conditions discussed in this chapter.
Homogeneous processes have the disadvantage of requiring about 50 to 80 ppm of iron in solution to be effective, concentration in many cases above of the permitted regulation (European Union allows maximum of 2 ppm Fe in the water treatment) [12], this strict regulation in the amount of dissolved Fe, implies that most of the time it is necessary to 106 Wastewater treatment using an iron nanocatalyst supported on Fique fibers have a secondary treatment to reduce the contaminant or to use higher concentration of dissolved Fe but implementing further processes to recover the remainder iron, turning the homogeneous processes into a costly treatment, suitable only under very specific conditions.
On the other hand, heterogeneous catalysis using solid supports allow to deposit the active phase (iron compounds) on their surface, facilitating the retrieving of the catalyst from the reaction solution, improving the mechanical resistance and in many case creating a synergetic effect that improves the chemical activity of the material. There have been reports of the use of different types of catalytic supports in the degradation of OII, ie. clays [13], silica [14], alumina [15], aluminosilicates [16], cation exchange resins [17], chelants [18], zeolites [19] and activated charcoal [20]. Nowadays the use of natural products as catalytic supporting materials is a trend, due to the interesting properties that these type of materials could have.
The use of nanosized iron compounds in the treatment of wastewater, takes advantage the high reactivity, increase surface area and synergic support-particle effects [21]. Particularly, the use of nanometric iron species in industrial water treatment have been reported to present the following advantages: i) efficiency in the treatment of effluents, ii) nanoparticles usage cycles, iii) environmental safety, iv) low cost of iron, v) strong adsorption capacity, vi) easy separation and vii) good stability [22].
The aim of this chapter was to evaluate the effect of crossed factors: pH, 퐶 , 퐶 푂퐼퐼0 퐻2푂20 and 퐹푒 푤푡. % the efficiency of OII dye degradation. A Box - Bhenken experimental design surface was used to identify the most important factors that affect the process, allowing obtain statistically significant empirical models.
In addition, under the most favorable operating conditions the effect of temperature, inhibitory concentration of chloride ions and stability of the catalyst, were evaluated. In order to analyze the obtained percentage of mineralization the total organic carbon (TOC) and the total nitrogen (TN) were determinate. 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 107
Materials and methods
OII degradation Based on the physicochemical properties characterized in the material synthesized in previous works, the impregnated material obtained on the functionalized fiber MC3 (denominated catalysts hereinafter) was selected to be tested in the catalytic experiments on the degradation of OII. The resulted catalysts have iron loadings of 10.9, 13.2 and 14.9wt%, quantified by FAAS.
The catalytic oxidation reaction was performed in a jacketed glass batch reactor (500 mL), kept under constant agitation (240 rpm). Each run lasted 240 minutes; used 800 mg of catalyst contained in paper bags (with pore size: 0.45μm, dimensions: 450x500x0.8mm, permeability: 1500 L/m2.s, material: thermosetting filter paper for tea bags [23]) in contact with 250 mL of an OII solution (C16H11N2NaO4S, Sigma -Aldrich®), experiments were performed at 20oC; Values of the experimental pH, OII solution concentration, hydrogen peroxide concentration and iron loading on the catalyst were set according within the limits of the ranges reported in Table 4.1 and the design of experiments summarized in Table 4.2.
All experiments were performed ensuring that the predominant mechanism of the process was the oxidation reaction and not mass transfer [24,25]. For this, the Weisz – Prater criterion was used [26], which establishes that for CWP << 1 there are not internal diffusion. The agitation level was kept 240 rpm because ensures the Weisz – Prater criterion and was not strong enough to caused mechanical damage to the catalyst. In order to meet the criterion Cwp the catalyst size was reduced to a particle size of 8mm in which Cwp << 1 was fulfilled. Agitation and catalyst particle size was also set to ensure that the effect of diffusion resistances from the bulk of the reaction solution to the catalyst surface were eliminated.
A set of experiments was performed implementing a Box- Bhenken design of experiments (DOE) with response surface, which used the maximum and minimum levels of the four factors evaluated in the degradation of the dye Orange II (see Table 4.1), with triplicate on the center point, for a total of 27 experiments. The ranges considered for the operating variables were chosen after making an intensive literature review [19,27-29], these conditions are representative of those founded in industrial wastewater effluent. 108 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
MiniTab 16 Statistical Software served to identify the contribution of each variable and its interaction in the degradation of the dye OII through the respective statistical analysis of the data obtained. Statistical regression was used to fit a second order polynomial experimental data and identify relevant terms of the model (equation (1)).
2 푌 = 훽0 + ∑ 훽푖푥푖 + ∑ 훽푖푖푥푖푖 + ∑ 훽푖푗푥푖푥푗 퐸푞 (1)
Where β0 is the compensatory term; βi is dependent term or the linear effect of factor input xi; ii is the quadratic effect input factor xi and βij is the effect of interaction between the linearly linear input factor xi and xj.
Table 4.1. Factors evaluated in the dye degradation of OII using iron supported on fique catalyst 22 Level Factor Low Medium High pH 2.5 3 3.5 [OII]o (M) 2푥10−5 1.1푥10−4 2푥10−4 −4 −3 −2 [H2O2]o (M) 1푥10 5.05푥10 1푥10 Fe wt.% 10.9 13.2 14.9
For each run the values of the variables pH, temperature and initial concentration of dye were set then reaction was started by adding the hydrogen peroxide solution (Merck). The pH was measured with a pH meter (Toledo LE427), the initial pH of the solutions to be treated was adjusted with the addition of 0.1M NaOH or 0.1M HCl.
The reaction advance was continuously monitored using an UV-vis spectrophotometry to track the absorbance the OII molecule in a quartz cell; OII concentrations were assessed through a calibration curve obtained at a wavelength of 486nm (See annex 3).
The degradation percentage of the dyes was expressed as the equation (2):
퐶 − 퐶 퐷푒𝑔푟푎푑푎푡𝑖표푛 (%) = 표 푥 100% 퐸푞 (2) 퐶0 where C0 is the initial concentration of the dye (mg /L) and C is the residual concentration of the dye (mg /L). 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 109
Upon completion of each experiment an aliquot of the treated solution was taken in order to assess the stability of the catalyst, the amount of iron leached was quantified by flame atomic absorption spectrometry (FAAS) using the injection method in a Hitachi z-8000 atomic absorption spectrometer equipped with an atomizer with air/acetylene burner used for the determination of elemental iron. The wavelength used for the determination of the analyte was: Fe 248.3nm.
The DOE conditions that provided one of the highest OII degradation were used to perform two new sets of experiment, the first once investigates the effect of temperature in the degradation reaction, in this case, degradation experiment were done at 30, 50 and 70oC. The second set of experiments comprised continues cycles of reaction at 20oC (up to 7 cycles), in which the very same catalyst was reuse.
Effect of chloride ion Several studies have reported contradictory effects of the concentration of ions in the reaction solution for the oxidation of Orange II, in particular the effect of Cl- ion have been reported to both to have beneficial and detrimental effects that seem to be dependent of the ion concentration and the type of catalyst used [27-29]. Based on this evidences a set the experiments run under the pH, H2O2 and Orange II concentration and iron catalyst loading that give the third highest Orange II degradation in the DOE, along with three different level of chloride ions in concentrations ranging from 0 to 1푥10−2M were performed.
Total Organic Carbon (TOC) and Total Nitrogen (TN) analysis Considering that OII degradation monitored by UV-vis spectrophotometry does not enable to determine if there was complete oxidation of the dye molecule. Two type of analysis were implemented to verify the advance of the chemical oxidation in the degradation process, TOC and TN analysis were performed on a Shimadzu TOC-VCHS/CSN analyzer following the Clean Water Act Analytical Methods 352.1 [30], 353.2 [31] and 410.4 [32] approved by EPA (US Environmental Protection Agency). TOC and TN were done on sample taken from the reaction solution (before and after reaction) of an experiment performed at the operating conditions the DOE showed to be the third highest terms the Orange II degradation. 110 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Identification of intermediate products resulting from the treatment of OII High pressure liquid chromatography (HPLC) was used to identified the possible intermediate compounds generated during the reaction of Orange II degradation, an Agilent Technologies 1260 Infinity chromatograph was used; the chromatograph was fitted with a Jupiter 5μm C18 300Å column, made of stainless steel with measures of 250 x 4.6 mm. The separated compounds were analyzed by a detector 325 Dual Wavelength UVVis. The mobile phase used was a methanol and water in relation 95:5, flow was set as 1 mL.min-1 with injection volumen of 20 μL and the linear gradient shown below was established: t = 0, H2O = 95, metOH = 5 ; t = 20, H2O = 30, metOH = 70; t = 25, H2O = 95, metOH = 5; t = 28, H2O = 95, metOH = 5.
Results and discussion
OII degradation Preliminary experiments were performed to verify if any percentage of degradation could be attributed to dye adsorption on the catalyst and/or on the paper bags containing the catalyst (Experiments 1 and 3 in Figure 4.1). Neglectable degradation values were obtained, 0.1 and 0.03% degradation for the catalyst contained in the tea bag experiments, respectively. This small values demonstrated that dye adsorption or oxidation on the catalyst and/or on paper bags is not important in the degradation process. Also, Figure 4.1 shows the important effect of H2O2, without the presence of H2O2 the advance of the reaction is essentially null, indicating that the sole presence of Fe+3 in the catalyst is not enough to drive the degradation of OII.
Additionally, the homogenous H2O2 oxidation capability was determine by performing an experiment in which not catalyst was added (Experiment 2, Figure 4.2); it was conclude that for the operating condition of the experiment the H2O2 has a contribution in the order of 0.3%. The results of the experiments presented in Figure 4.2 shows that the variables
H2O2, catalyst and paper bags applied independently have not major effect in the 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 111 degradation OII. 0,4 Experiment 1 Experiment 2 0,3 Experiment 3
0,2
0,1 Degradation(%) 0,0 0 30 60 90 120 150 180 210 240 Time (min) Figure 4.1. OII degradation after 4 hours of catalytic activity performed under the following −4 conditions: Experiment 1 (Catalyst Fe10.9 wt.% and Dye 퐶푂퐼퐼0: 2푥10 푀), Experiment 2 (Dye 퐶 : 2푥10−4푀 and oxidizing agent 퐶 : 5.05푥10−3푀), Experiment 3 (Catalyst 10.9 푂퐼퐼0 퐻2푂20 −4 Fe wt.%, Dye 퐶푂퐼퐼0: 2푥10 푀, catalyst contained in aromatic bag28 Figure 4.2 shows a typical OII degradation curve under the typical experimental conditions used in this study. Two stages in the degradation process are identified, an initial very fast degradation section for reaction time before 30 minutes, characterized by the conversion of Fe+2 into Fe+3 [26]. Followed by a long and slow degradation process after 30 minutes
+3 where Fe is found primarily in the Fe , denominated Fenton – Like. The first stage is an unstable state that depends of the initial catalyst characteristics and reaction solution characteristics (iron loading, iron compound reduction/oxidation state, ions dissolved in the solution, among others) and is frequently considered to be a catalyst conditioning period. Essentially, the possible mechanisms of reaction are limited to those proposed in the literature which take into account ferric and ferrous ions, then the effect may have been zero valent iron was not analyzed, as it is beyond the scope of this investigation.
1,0
0,8
0,6
0,4
COII/COIIo 0,2
0,0 0 30 60 90 120 150 180 210 240 Time (min) Figure 4.2. OII degradation after 4 hours of catalytic activity performed under the following conditions: pH: 2.5, 퐶 : 1.1푥10−4푀, 퐶 : 5.05푥10−3푀 and 10.9푤푡. % 29 푂퐼퐼0 퐻2푂20 112 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
The characteristic shape of the degradation curve reported in Figure 4.2 is typical of materials with low surface area and low porosity, as the ones characterized in this work. This behavior is due to the easy accessibility of Fe+3 ions to react with OH• radicals and promotes immediate oxidation reaction and therefore degrading the contaminating dye.
Table 4.2 summarizes the experimental conditions of each one of the 27 runs (pH, 퐶푂퐼퐼0, 퐶 , Fe wt.% has 3 different levels: high (1), medium (0) and low(-1)), included tests to 퐻2푂20 determine crossed factor effects and also include the three center point runs. These experiments were performed randomly to minimize possible systematic errors that can be generated (All experimental results are in the Annex 4). Table 4.2. Experiments values of Box - Behnken experimental design, degradation percentage obtained for each experimental conditions 23 Run Ph COIIo (M) H2O2 (M) Fe wt.% %Deg 1 0 -1 1 0 5.91 2 0 0 0 0 6.83 3 -1 0 0 1 81.94 4 1 0 0 -1 19.67 5 1 0 0 1 1.22 6 0 1 -1 0 1.28 7 0 1 1 0 0.56 8 -1 0 0 -1 93.23 9 0 -1 -1 0 53.30 10 1 1 0 0 0.23 11 -1 -1 0 0 94.50 12 -1 1 0 0 62.96 13 0 0 0 0 27.98 14 1 -1 0 0 5.43 15 0 0 1 -1 60.19 16 0 0 -1 1 4.31 17 0 0 1 1 3.49 18 0 0 -1 -1 40.31 19 0 -1 0 1 49.05 20 1 0 1 0 4.23 21 0 1 0 1 0.30 22 0 0 0 0 20.08 23 -1 0 -1 0 86.72 24 1 0 -1 0 20.27 25 -1 0 1 0 95.61 26 0 1 0 -1 2.24 27 0 -1 -1 -1 7.28 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 113
The statistical adjustment of the equation decribed previously (equation (1)) to the data summarizes in Table 4.3, leads to the experimental description of the degradation
(equation (3)); where A:pH, B: COIIo, C: H2O2 and D: Fe wt.%.
퐷푒𝑔 (%) = 1571.83 − 755.377A − 306406B + 13859.4C − 47.2442D + 114.042퐴2 − 846940966퐵2 + 195140퐶2 + 2.04457퐷2 + 146307AB Eq (3) − 2517.69AC − 0.68625AD + 26190702BC − 15441.8BD
− 843.564CD
(3)
Table 4.3. Analysis of variance (ANOVA) for percentage of degradation by MiniTab 16 Statistical Software24 Source DF Seq SS Adj SS Adj MS F P Regression 14 27807.8 27807.8 1986.3 6.45 0.003 Linear 4 19908.6 13143.6 3285.9 10.67 0.001 A: pH 1 17933.4 11805.3 11805.3 38.35 0.000 B: COIIo 1 1823.4 950.6 950.6 3.09 0.109 C: H2O2 1 109.2 15.1 15.1 0.05 0.829 D: Fe wt.% 1 42.6 372.7 372.7 1.21 0.297 Square 4 6500.8 6500.8 1625.2 5.28 0.015 AA 1 5681.9 4335.2 4335.2 14.08 0.004 BB 1 343 251 251 0.82 0.388 CC 1 199.5 121.9 121.9 0.40 0.543 DD 1 276.4 276.4 276.4 0.90 0.366 Interaction 6 1398.4 1398.4 233.1 0.76 0.619 AB 1 173.4 173.4 173.4 0.56 0.470 AC 1 155.3 155.3 155.3 0.50 0.494 AD 1 3.2 3.2 3.2 0.01 0.921 BC 1 544.6 544.6 544.6 1.77 0.213 BD 1 52.1 52.1 52.1 0.17 0.690 CD 1 469.9 469.9 469.9 1.53 0.245 Total 26 30957.0
Additionally, the interaction A2 also related to the pH indicates the presence of a curvature in the model and thereby the possible existence of maximum degradation value within the range of variables studied (Show in the Annex 5). Given the high efficiency obtained in the degradation, it was concluded that the levels analyzed were adequate. The model shows a good fit of the experimental and the calculated data, reflected by the correlation coefficient R2 = 90.06% and R2 adjusted = 74.15%. 114 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
100 80 60 40
20 Deg (%) calc (%) Deg 0 0 20 40 60 80 100 Deg(%) exp Figure 4.3. Experimental and calculated results of the experimental design for Orange II oxidation. Degradation Response (%).30
In order to determine the appropriate fitting data regression and analysis of variance (ANOVA), analysis of residual plots that are defined as the difference between the set values (model) and the observed values (experimental) was performed. Residual Plots for % Deg a) Normal Probability Plot b) Versus Fits 99 30
90
15
l
t
a
n
u
e
d c 50 i
r 0
s e
e b) P a) R 10 -15
1 -30 -30 -15 0 15 30 0 25 50 75 100 Residual Fitted Value
c) Histogram d) Versus Order 8 30
6 y 15
l
c
a
n
u
e
d i
u 4 0
s
q
e
e r c) R d) F 2 -15
0 -30 -24 -12 0 12 24 2 4 6 8 10 12 14 16 18 20 22 24 26 Residual Observation Order
Figure 4.4. Residual plots for kapmod a) Normal probability plot, b) Versus fits, c) Histogram and d) Versus order31
As shown in Figure 4.4a residues, follow a normal distribution, half of data takes positive values (over 50%) and the other half negative values (below 50%), which allows to conclude that there are no significant deviations of residuals from the normal distribution. Figure 4.4b, 4.4c and 4.4d allow to verify the homocedasticity of the residuals (constant variance) meaning they are symmetrically distributed and are not interdependent to each other. 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 115
Figures 4.5, 4.6 and 4.7 allows to observed the combined effect of the experimental variables catalyst loading (Fe wt.%),H2O2 and COIIo concentration when paired with the pH variable, a local maximums is always observed at pH = 2.5. although most of the literature reports that for pH values below 3 Fenton oxidation becomes less effective due to the regeneration of Fe+2 is inhibited by the formation of intermediate products such as
+ hidroxiperoxonium radicals (H3O2 ) [26]. This low pH catalytic activity seems to be unique for the combination of iron supported on fique fiber and turning this catalyst into a very attractive catalyst for specific applications at low pH.
In pH values between 3 and 3.5 degradation did not achieved good results (just in the range between 0 to 20%), which could be related to the great dependence of the iron oxidation state as a function of pH; indicating that under these pH conditions Fe+2 may not be present in enough concentration, hindering its reaction capability with hydroxyl groups and affecting the Fe+2 to Fe+3 cycle necessary for the degradation reaction to take place, and boosting the formation of competitive intermediates such as FeOOH [19].
Although the effect of the concentration of H2O2 it was determine to be a factor with not statistical significance, it can be observed in Figure 4.5 that the combination of factors pH and H2O2 is particularly important at low pH levels, emphasizing the significant effect the low pH has for this type of catalyst (Figure 4.5).
퐶6퐻11푁2푁푎푂4푆 + 42퐻2푂2 → 2퐻푁푂3 + 푁푎퐻푆푂4 + 46퐻2푂 + 16퐶푂2 퐸푞 (4)
Equation (4) relates the theoretical number of moles of oxidizing agent required to degrade 1 mol of OII dye [35], all concentrations used in the experimental design have values above to the stoichiometric amounts required for complete mineralization.
So the concentration of H2O2 and the percentage degradation are directly proportional as a result of competition by hydroxyl radicals, Figure 4.5 shows that even the lowest amount of peroxide managed to have good performance in the percentage degradation. At low pH value for any H2O2, the degradation obtained is above 80%, which implies, in terms of application, that using low H2O2 concentration will render high degradation, while keeping
H2O2 at the minimum possible.
-3 From Table 4.2 can be observed that the H2O2 medium level concentration (5.05x10 M) generates high degradation percentages in combination with low pH level (runs 3, 8 and 11), rendering degradation values of 81.94, 93.23 and 94.5%, respectively. 116 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Figure 4.6 shows the combine effect of the catalyst Fe loading and pH; once again, only at low pH value (pH = 2.5) the catalyst Fe loading showed significant OII degradation, emphasizing the pivotal role pH has in the reaction. Although the iron loaded to the catalyst could be significant different (from 10.9 to 14.9 wt.%), the degradation obtained for any catalyst at low pH is also above 80%, being this an additional evidence of the complex network of reactions happening in the Fenton process. Iron role in the Fenton reaction have been related to the net balance of OH• radicals available to react, a low iron concentration available to react, will have a negative effect in the degradation because there will be also low concentration of OH• ready to react, and the opposing effect will happen as the iron available to react increases, however an excess of iron could also interfere negatively with the Fenton reaction [19].
Figure 4.5. Contour plot of Degradation (%) vs H2O2 and pH 32 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 117
Figure 4.6. Contour plot of Degradation (%) vs %Fe and pH 33
Figure 4.7. Contour plot of Degradation (%) vs COIIo and pH 34
OII initial concentration showed a negative effect on the degradation process (Figure 4.7), because at higher initial concentrations of dye more time is required for degradation, the degradation percentage decreases and increases the formation of intermediates, which is consistent with results obtained by other authors [16,25]. If the initial concentration of dye 118 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
−5 −4 is high (2푥10 − 1.1푥10 푀 ), the amount of available H2O2 molecules could be considered to be constant, reducing the possibility of interaction between OII/ OH• [25].
The extensive work performed on the determination of OII degradation on iron/modified fique fibers catalysts and the robust and rigorous statistical support provided by the Box – Behnken DOE allow to identified a potential set of operating conditions that would reach high degradation percentages, while reducing the consumption of H2O2, iron loading, examining the effect of Orange II initial concentration and optimizing pH (pH: 2.5, COII0: 1.1x10−4M, C : 5.05x10−3M and 10.9 Fe %wt). This operating condition will be used in H2O20 the chloride ions, temperature effect and deactivation experiments.
Many attempts have been made to described the reaction mechanisms of the heterogeneous Fenton reactions, but due to intricate interaction of intermediate species, effect of pH in the net balance of OH• in solution and the simultaneous action of consecutive, parallel and in some case competitive reactions, not a clear kinetic equation that broadly describe this phenomena has been tested.
Figure 4.8. Degradation OII, the left part initial color and the right the color after the treatment under the conditions: pH: 2.5, C : 1.1x10−4M, C : 5.05x10−3M and OII0 H2O20 10.9 Fe wt. %)35
Relevant approaches have been done in order to produce semi-empirical equations useful for scaling up and reactor design. Kinetic model based on Fermi’s function has shown to properly describe Fenton processes in which the degradation evolution shows a sigmoidal characteristic curve, related for particular reaction conditions, type of catalyst and 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 119 contaminant molecule [16]. None of the degradation curve in this study showed a sigmoidal curve, on the contrary the behavior for most of them was some sort of exponential decay, for this case a simplified pseudo-first-order kinetic could be proposed [36].
+3 The catalytic degradation of OII based in Fe /H2O2, can be described from the mass balance corresponding to a batch reactor relative to the concentration of OII, considering perfect mixing, as follows equation (5):
푑퐶푂퐼퐼 − = 푘퐶 ∎퐶 퐸푞 (5) 푑푡 푂퐻 푂퐼퐼 where k is the rate constant, t is the degradation time, 퐶푂퐻∎ is the hydroxyl radicals concentration and 퐶푂퐼퐼 is the dye concentration at a given time. Like other authors [32, 35], Fenton oxidation studies is assumed that the concentration of OH• is constant along each of the runs, which allows to write the equation (6):
(−푟푂퐼퐼) = 푘푎푝퐶푂퐼퐼 퐸푞 (6)
kap values can be calculated from the experiments performed by the DOE, after linearizing the data from the integration of the mass balance equation (equation (5)), evaluated between the limits (t0=0, C0) and (t, C). The integrated expression is:
퐶 −ln ( ) = 푘푎푝푡 퐸푞 (7) 퐶0
The pseudo-first order rate constants of degradation were calculated from linear regression - ln (COII / COIIo) vs time plots. The type of oxidation process studied occurs 2+ when H2O2 is brought into contact with Fe ions in solutions at acidic pH. The ferrous and ferric ions initiates the reaction of peroxide decomposition, which gives as results the
• ∎ generation of highly reactive radicals OH and perhydroxyl (퐻푂2 ), being the hydroxyl radicals the ones with greater oxidizing power (equations (8) and (9)) [39].
+2 +3 − 퐹푒 + 퐻2푂2 → 퐹푒 + 푂퐻 + OH • 퐸푞 (8)
+3 +2 ∎ + 퐹푒 + 퐻2푂2 → 퐹푒 + 퐻푂2 + 퐻 퐸푞 (9) Fenton's reactions are highly complex chemical combination of sequential and/or simultaneous reactions involving initiation, propagation, termination stages in which 120 Wastewater treatment using an iron nanocatalyst supported on Fique fibers oxidation and reduction cycles, simultaneous formation radical species with lower oxidizing power, in addition to the multiple radical species may be present at once; making the development of a mechanistic kinetic expression a very convoluted task. The results of the simplified pseudo-first-order kinetic analysis is reported in Table 4.4.
Table 4.4. Simplified pseudo-first-order kinetic analysis 25
-1 -1 -1 Run kap (min ) R² Run kap (min ) R² Run kap (min ) R² 1 2.31x10-4 0.951 11 9.78 x10-3 0.899 21 1.12 x10-5 0.719 2 2.90 x10-4 0.917 12 3.53 x10-3 0.942 22 8.08 x10-4 0.940 3 5.89 x10-3 0.997 13 1.10 x10-3 0.885 23 7.20 x10-3 0.962 4 5.76 x10-4 0.526 14 1.85 x10-4 0.760 24 9.99 x10-4 0.909 5 5.17 x10-5 0.954 15 3.41 x10-3 0.925 21 1.12 x10-5 0.719 6 4.17 x10-5 0.726 16 1.84 x10-4 0.979 25 1.17 x10-2 0.971 7 2.15 x10-5 0.918 17 1.56 x10-4 0.967 26 6.55 x10-5 0.700 8 9.20 x10-3 0.863 18 1.80 x10-3 0.919 27 2.53 x10-4 0.693 9 2.60 x10-3 0.673 19 1.82 x10-3 0.452 10 8.69 x10-6 0.908 20 1.91 x10-4 0.986
The simplified pseudo-first-order kinetic model is able to describe 8 of the degradation conditions with a R2 above 0.95, an additional set of 8 degradation conditions are describe by the simplified pseudo-first-order kinetic model a with a R2 above 0.90. It is quite remarkable that such a simple model could fit such a complex kinetics; out of the remaining 11 set of condition, 3 of them have R2 above 0.85; the remaining 8 degradation conditions have R2 below 0.75.
100
80
60 30°C 40 50°C 70°C
Degradation (%) Degradation 20
0 0 30 60 90 120 150 180 210 240 Time (min) Figure 4.9. Effect of temperature ions in OII degradation after 4 hours of catalytic activity under these conditions: pH: 2.5, 퐶 : 1.1푥10−4푀, 퐶 : 5.05푥10−3푀 and 10.9 퐹푒 %푤푡 36 푂퐼퐼0 퐻2푂20 In order to evaluate the influence of temperature on the degradation process, experiments were performed at different temperatures (30, 50 and 70oC), under the conditions that 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 121
were found to generate the third highest OII degradation in the DOE (run 8): pH: 2.5, 퐶푂퐼퐼0: 1.1푥10−4푀, 퐶 : 5.05푥10−3푀 and 10.9 퐹푒 푤푡. %. The results of this experiment are 퐻2푂20 shown in Figure 4.9.
The OII degradation profiles for 30 and 50oC have overlapping behavior reaching a 57% of degradation up to 30 minutes of reaction, form that point forward the profile obtained at 50oC shows a better performance, reaching almost 89% of degradation after 60 minutes of reaction, meanwhile the 30oC profile at the same time only reaches 67%. The 70oC profile over performs both the 30 and 50oC, reaching close to 94% of degradation in the initial 30 minutes. It is not surprising that temperature accelerates the degradation process, due to the exponential dependency of the Arrhenius factor with temperature, probably enhancing the OH• production and iron regeneration [25,34]. However, due to the large volume of wastewater usually generated with this type of contaminant, the option to use temperature to reduce the degradation time is not practical in terms of operating costs.
Catalyst stability was determine performing repetitive degradation cycles with the same catalyst and by taking samples, to be analyzed by FAAS, from the reactive solution at the end of each cycle.
100 Cycle 1 90 Cycle 5 80 Cycle 7 70 60 50 40 30
Degradation (%) Degradation 20 10 0 0 30 60 90 120 150 180 210 240 Time (min) Figure 4.10. Cycle number of use of OII degradation after 4 hours of catalytic activity under these conditions: pH: 2.5, 퐶 : 1.1푥10−4푀, 퐶 : 5.05푥10−3푀 and 10.9 퐹푒 푤푡. % 37 푂퐼퐼0 퐻2푂20 The result of the catalyst deactivation (continue degradation cycles, for a total de 28 hrs of reaction) are presented in Figure 4.10, out of the 7 cycles performed only cycle 1, 5 and 7 are shown, because the reduction in degradation between run 1 to 4 were small; from cycle 1 to 5 there was a reduction in the final degradation value in order of 10%, however 122 Wastewater treatment using an iron nanocatalyst supported on Fique fibers the reduction in the seventh run was considerable, reaching only 45% percent of degradation.
In terms of Fe lixiviated from the catalyst to the reaction solution, the average value of the amount of iron in solution for each run, corresponds to 0.822ppm (approximately 5.38% in weight of the impregnate iron), which is below the allowed by the European Union value which sets a maximum value of 2ppm [9], the Annex 6 reports the data obtained through FAAS. The low concentration of iron lixiviated found in the final reaction solution implies that the degradation reaction could be considerate essentially happening in the heterogeneous phase, on the contrary the amount of iron leached (in terms of percentage of impregnated Fe).
Figure 4.11 shows not significant changes in the crystallinity, iron phase and crystal size of both the before and after catalysts, meaning that deactivation observed in the reaction cycles it is not due to changes of the iron phase supported on the fiber.
1200
1000 After 800 Before
600
400 Intensity a.u. Intensity 200
0 5 8 11 14 17 20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 65 68 71 74 77 80 83 2 tetha Figure 4.11. XRD of catalyst before and after Orange II treatment38
Effect of chloride ion Real wastewater could containing a mixture of inorganic anions that significantly affect the degradation of OII. In literature the most reported effect is for the chloride ions; the results of a set the experiments run under the pH, H2O2, OII concentration and iron catalyst loading that give the second highest OII degradation in the DOE, along with three different levels of chloride ions concentrations are presented in Figure 4.12. 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 123
100
80
60
40 Chlorides 0M
20 Chlorides 0.005M Degradation (%) Degradation Chlorides 0.01M 0 0 30 60 90 120 150 180 210 240 270 Time (min) Figure 4.12. Effect of chloride ions in OII degradation after 4 hours of catalytic activity under these conditions: pH: 2.5, 퐶 : 1.1푥10−4푀, 퐶 : 5.05푥10−3푀 and 10.9 퐹푒 푤푡%39 푂퐼퐼0 퐻2푂20 Figure 4.12 shows the significant influence the concentration of chloride ions have on the degradation of OII, especially in the initial 30 minutes of reaction, being this another evidence of the previous mentioned catalyst condition stage. For the time range from 0 to 180 minutes the free chloride ion experiment outperforms the 0.005 M experiment, form that time on both experiments follow almost an overlapping behavior; meanwhile in the case of the 0.01 M the free chloride ion experiment outperforms it in the whole reaction time.
There have been reports related to the reduction in the OH• oxidative capability caused by chloride ions inhibition, resulting in an increment of H2O2 consumption (equation 10 and 11) affecting the iron species reducing cycle and generating products containing chloride ions [41].
퐶푙− + 퐻푂• → 퐶푙퐻푂•− (10)
퐶푙퐻푂•− + 퐹푒+2 → 퐶푙− + 퐻푂− 퐹푒+3 퐸푞 (11)
Total Organic Carbon (TOC) and Total Nitrogen (TN) analysis The extent of OII mineralization (the process through which an organic substance becomes CO2 and water) [42] was determinate by TOC and TN. Table 4.5 summarizes the TOC and TN results obtained; the total nitrogen reduction only reached 28.6% and TOC value was reduced in a 55.4%, the fact that the Orange II molecule is a molecule with extensive organic chemical groups units (nitro, hydroxyl, sulfonic, as shown in Figure 4.13) made the mineralization of OII a very demanding process. 124 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 4.5. Total Organic Carbon (TOC) and Total Nitrogen (TN) analysis results 26 Sample TN (mg/L) TOC (mg/L) Dye Orange II in solution (0.2mM) 1.739 44.89 Water treatment 2.437 20.04 Reduction (%) 28.6 55.4
Figure 4.13. Structural formula of the azo dye Orange II [38]40
The result of the TOC and TN indicates that, although there was an important fractioning of the OII molecule, not a 100% of dye mineralization was achieved meaning that the azo bond (-N=N-) was in fact attacked by the oxidizing species, however intermediates species generated by the (-N=N-) breaking were not totally oxidized, on the contrary TOC and TN results reveal that intermediates.
In order to identify which intermediates are presented after dye degradation, HPLC chromatography was performed, Figure 4.14. shows the main absorbance band of OII in the UV-Vis region is situated at 483nm, these are chromatograms of before and after reaction using the catalyst of iron nanoparticles supported on fique fiber. Clearly the strong absorption at 483 nm was drastically reduced after the treatment, confirming that the chromophore bond N = N bond is completely broken, its decrease is due to degradation of the aromatic portion of the dye, as these are easier to destroy compared to aromatic rings [43]. 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 125
80
70
60
50 Before 40 mUA After 30
20
10
0 0 5 10 15 20 25 Time (min) Figure 4.14. Chromatogram obtained with a UV-Vis detector at 483 nm of OII dye before and after degradation 41
140
120
100 Before 80 After
60 mAU 40
20
0 0 5 10 15 20 25 Time (min) Figure 4.15. Chromatogram obtained with a UV-Vis detector at 230 nm related with benzene 42 126 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
30
25
20
Before 15
After mAU 10
5
0 0 5 10 15 20 25 Time (min) Figure 4.16. Chromatogram obtained with a UV-Vis detector at 310 nm related with naphthalene 43
Two other bands at 230 nm and 310 nm are attributed to another intermediates as benzene and naphthalene rings adjacent, as shown in Figure 4.15 and 4.16 respectively. However, Figure 4.15 does not show a significant change in the presence of benzene, while the Figure 4.16 evidences the apparition of a new peak after the reaction took place, which allows to conclude that the amount of naphthalene present in solution increases [44].
Conclusions The effects of the reaction conditions on the degradation of OII on iron supported on modified fique fiber catalysts was studied. A Box-Behnken design of experiments allowed to determine the individual and the combined interaction of the main factor studied (pH, 퐶 , 퐶 and 퐹푒 푤푡. %). A maximum OII degradation of 95.61% was obtained operating 푂퐼퐼0 퐻2푂20 at pH: 2.5, 퐶 : 1.1푥10−4푀, 퐶 : 1.1푥10−2푀 and 13.2 %퐹푒 푤푡., the second highest 푂퐼퐼0 퐻2푂20 degradation value (93.23%) was obtained working at the same pH, 퐶푂퐼퐼0 but at lower 퐶 and %퐹푒 푤푡; the second operating conditions generated a slighter lower 퐻2푂20 degradation but using half of the H2O2 and with a catalyst of only 10.9% of iron, making it an interesting option from the engineering point of view. The presence of inhibitory chloride ions had a not so significant negative effect (reduction only 10% compared to the maximum degradation reached), temperature show to have a positive effect on the degradation process. However TOC and TN experiment showed that not complete mineralization was achieved in any of the experimental conditions tested. 4. Heterogeneous Fenton oxidation of Orange II using iron supported on modified fique catalyst s 127
Contour plots allowed to have a better understanding of the combined effects of 퐶푂퐼퐼0, 퐶 and 퐹푒 푤푡. % as a function of pH, which was statically determinate to be the variable 퐻2푂20 whit the highest impact in the process. Low pH level (2.5) was found to be the most favorable condition for Orange II degradation, being this some of the lowest pH values found in literature for heterogeneous Fenton reactions, converting the novel iron/modified fique fiber catalyst into a very attractive alternative for specific applications at low pH.
A simplified pseudo-first-order kinetic model was proposed and was able to describe 16 of the degradation conditions with a R2 above 0.9; a very remarkable result for such a simple model.
The effect of the presence of chloride ions in the reaction solution were evaluated, results show that concentrations as low as 0.005 M reduces the rate of OII degradation but after 4 hrs of reaction reaches the same OII degradation that the chloride ions free experiment. On the contrary, the 0.01 M of chloride ions OII degradation test underperforms in the whole extension of the experiment.
Catalyst stability was outstanding up to the initial 4 reaction cycles, but strongly decreased after subsequent cycles; Fe lixiviation from the catalyst to the reaction solution was in the order of 5.38% of the impregnated iron and may explain the loss of catalytic activity after several reaction cycles.
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5. Studies on adsorption mercury from aqueous solution on biocomposite material from fique fiber and iron nanoparticles 131
Chapter 5. Studies on adsorption mercury from aqueous solution on biocomposite material from fique fiber and iron nanoparticles
Abstract: The adsorption of mercury ions from aqueous solution onto an adsorbent (fique fiber with iron nanoparticles) is studied. In particular, were analyzed the effect of pH, initial concentration of mercury ions ([Hg+2]) and load of iron in the adsorbent material (Fe wt%). It is evident from a design response surface experiments (Box-Behnken) that in the mercury adsorption, the chemisorption mechanism predominates respect to physisorption. Langmuir and Freundlich isotherms were used to describe the physical adsorption of mercury, however they failed to properly described most of the experimental isotherms obtained. One simplified kinetic models, pseudo-second order, was tested to investigate adsorption mechanisms. It was found that the kinetics of adsorption of mercury onto the surface of the fique fiber with iron nanoparticles is described by the pseudo-second order model supporting chemisorption (chemical reaction) as rate controlling mechanism which indicates that the adsorption process is irreversible. pH has no apparent effect on adsorption In the range of pH 4 to 7; however, for pH greater than 8, the adsorption capacity increases as the pH value also increase.
Keywords: Furcraea andina, iron nanoparticles, mercury, adsorption, removal
Introduction Mercury is considered one of the most harmful metals in the environment due to their toxicity on a wide spectrum of flora and fauna, affecting human health as a result of bioaccumulation in the food chain [1], accumulation of mercury on human organs and 132 Wastewater treatment using an iron nanocatalyst supported on Fique fibers tissue cause critical disabilities, such as Minamata disease [2]. Mercury in the environment has two major sources, the first is one is denominate naturogenic (eruptions and geothermal activities) and provides a minimum percentage in relation to the total amount of pollutant mercury; the second form is the anthropogenic sources, which includes combustion, mining and disposal of industrial processes.
Indiscriminate and in many cases illegal gold mining in Colombian Amazonas river have showed to affect Amazonian ethnic groups, which have been tested to have the highest level of mercury poisoning in Colombia, having bioaccumulate Hg between 15.4 and 19.7 parts per million (ppm) [3], when the EPA has set a maximum contaminant level of this 2 parts per billion (ppb) [4].
It is of great interest to remove this pollutant from wastewater and several types of processes have been proposed such as: precipitation [5], coagulation [6], cementation [7], ultrafiltration [8], solvent extraction [9], photocatalysis [10], adsorption[11] and ion exchange [12], have been implemented within the possible alternatives to solve this problem. However, currently mercury removal remains a problem due to the lack of effective and economical, technologies that minimize energy and reagents consumption while increasing the selectivity towards mercury removal [13]. Out of the mercury removal technologies listed above, adsorption is the most used due to its simple operation, removal efficiency, selectivity, high adsorption rate and availability of materials with favorable properties to perform the process [14]. Many solid materials have been used as adsorbents such as extracellular biopolymers [15], cellulosic materials [16], zeolites [17], aluminosilicates [18], nanomaterials [19] and activated carbons [14].
Particularly materials such as iron nanoparticles have been reported to have magnetic properties, electrostatic charge, size, dispersion and homogeneity, which make them excellent choices for the adsorption of heavy metals. Likewise, the lignocellulosic materials enhance its adsorption capacity by the surface modification through loads or ligands that improve stability of the adsorbate and selectivity, these two alternative adsorbents are effective and inexpensive for quick removal and recovery of ions metal in sewage effluent.
The main goal of this study was to investigate the removal of Hg+2 from an aqueous solution using as adsorbent iron nanoparticles supported on fique fiber. Evaluating the influence on the removal of important factors such as initial concentration of mercury, 5. Studies on adsorption mercury from aqueous solution on biocomposite material from fique fiber and iron nanoparticles 133 solution pH and the iron loading in the adsorbent material. Chemical and physical adsorption models were used to adjust the experimental data.
Materials and methods Mercury solutions of 150mL and adsorbent material (iron nanoparticles supported on fique fiber) were arranged in a jacketed glass batch reactor, with continuous agitation (240rpm) controlled by the motor IKA 260. Each run lasted 30 minutes; all experiments were performed at 20°C and 551mmHg. The concentration of mercury remnant in the solution was determined by cold vapor atomic absorption spectrometry (CVAAS) using the injection method of an aliquot of 1000µL, in a Hitachi z-8000 atomic absorption spectrometer equipped with hydride generator. The wavelength used for the determination of the analyte was: Hg 253.7 nm.
Preliminary experiments were performed in order to determine the proper amount of of adsorbent material to use in the experiments (400, 800, 1000 and 1500 mg). The tested amount of material was submerged in a 150mL solution of 10 mg.L-1 mercury (II) with an initial pH = 10, at 20°C and 551mmHg, samples of the solution were taken upon time and analyzed via cold vapor atomic absorption spectrometry.
A Box- Bhenken design of experiments with response surface (DOE), which used the maximum and minimum levels of the three factors evaluated in the mercury removal was implemented, this type of DOE includes a triplicate center point, for a total of 15 experiments. A summary of the experimental condition for the DOE area presented in Table 5.1.
MiniTab 16 Statistical Software served to identify the contribution of each variable and its interaction in the removal of mercury through the respective statistical analysis of the data obtained. A linear regression method as the one described in equation (1) was used to set the second order polynomial experimental data and to identify relevant terms of the model.
2 푌 = 훽0 + ∑ 훽푖푥푖 + ∑ 훽푖푖푥푖푖 + ∑ 훽푖푗푥푖푥푗 퐸푞 (1)
Where β0 is the compensatory term; βi is dependent term or the linear effect of factor input xi; ii is the quadratic effect input factor xi and βij is the effect of interaction between the linearly linear input factor xi and xj. 134 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 5.1. Factors assessed in mercury removal using a adsorbent from Fique and iron nanoparticles27 Level Factor Low Medium High pH 4 7 10 [Hg]o (ppm) 1 10 14 Fe wt.% 10.9 13.2 14.9
Before the adsorption experiments were started, the solution initial Hg concentration and pH was measured via vapor atomic absorption spectrometry and a Toledo LE427 pHmeter, respectively. The initial pH of the solution was adjusted with the addition of different buffers: citrate (pH=4), phosphate (pH=7) and ammoniacal (pH =10). Then the adsorbent material was added to the solution .
The adsorption capacity of the metal ion in solution was determined for each value of initial concentration, with experimental data equilibrium concentration and initial concentration, using the following equation (2):
(퐶 − 퐶 )푉 푞 = 푖 푒 퐸푞 (2) 푒 푤
Where qe is the adsorption capacity (mg/g), Ci is the initial concentration of solute (adsorbate) in solution (mg/L), Ce is the solute concentration in the equilibrium (mg/L), V is the mercury solution and W is the adsorbent mass (g).
The removal percentage of the mercury was expressed as the equation (3): 퐶 − 퐶 푅푒푚표푣푎푙 (%) = 표 푥 100% 퐸푞 (3) 퐶0 Results and discussion Figure 5.1 shows the results obtained in the evaluation of the adsorbent dosage in Hg removal; the smallest mass of adsorbent material (400mg) achieved just a 15% mercury removal. It was found that an increase in the amount of adsorbent material (with pH and Hg concentration constant) has a positive effect on mercury removal, which agrees with 5. Studies on adsorption mercury from aqueous solution on biocomposite material from fique fiber and iron nanoparticles 135 other studies in which the same trend has been evident removing pollutants from waste water [20,21], this behavior is explained as a result of greater availability of surface area and functional groups.
70
60
50
40
30 Removal Removal (%) 20
10
0 0 10 20 30 40 50 60 Time (min) 400 mg 800 mg 1000 mg 1500 mg
Figure 5.1. Percentage of removal at different loads of adsorbent material (pH=10, initial concentration of mercury = 10ppm and 10.9 wt.% Fe)44
Experiments ran with 800, 1000 and 1500mg of adsorbent material showed approximated final removal values of 53, 56.7 and 66.5%, respectively. However, when the final Hg removal obtained for each experiments is plotted as a function of the amount of adsorbent (Figure 5.2), it shows an apparent saturation point, which is an unexpected behavior not common for physisorption processes in which the only variable changing is the amount of adsorbent material, where a more lineal behavior would be expected. 136 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Figure 5.2. Final removal percentage of removal at different loads of adsorbent material (pH=10, initial concentration of mercury = 10 ppm and 10.9 wt.% Fe) 45
Analyzing the results obtained for the 800 and 1500mg experiments, the 1500 mg (using almost the double of 800mg) shows just a 13% of mercury removal when compare against the 800 mg experiment; in terms of industrial application would imply a reduction in the amount of material required and possibly a decrease in costs; under this perspective the 800mg of adsorbent material was the chosen amount to perform the upcoming experiments.
The first of them is to determine the adsorption capacity of the raw fique fiber and to have it as baseline experiment, Figure 5.3 shows the typical profile adsorption isotherm with a final removal value in the order of 24%, below the 53.7% reported for the same amount of adsorbent material (10.9% Fe on modified fique fiber) under the very same conditions, of pH, initial Hg concentration, temperature and agitation, implying a positive effect of the fiber modification and the presence of iron nanoparticle son the fiber surface. 5. Studies on adsorption mercury from aqueous solution on biocomposite material from fique fiber and iron nanoparticles 137
35 30 25 20 15
% Removal % 10 5 0 0 10 20 30 40 50 60 Time (min) Figure 5.3. Mercury removal using raw fique fiber (pH=10, initial concentration of mercury =10ppm).46
With the purpose to evaluate the experimental data obtained, two typical physisorption model were fitted, Langmuir [22] and Freundlich [23], this type of model, if properly describe the experimental data, could provide information about aspects such as adsorption mechanism, surface properties and affinity between adsorbate and adsorbent.
Table 5.2. Adsorption isotherms models 28 Model Linealization form Langmuir 푞푚퐾퐿퐶푒 퐶푒 1 1 푞푒 = (4) = + 퐶푒 (5) 1 + 퐾퐿퐶푒 푞푒 푞푚푏 푞푚 Freundlich 1/푛 1 푞푒 = 퐾푓퐶푒 (6) log 푞 = log 퐾 + 푙표𝑔퐶푒 (7) 푒 퐹 푛 where qe is the adsorption capacity (mg/g), Ce is the equilibrium concentrations of mercury
(mg/l) in the solution, qm (mg/g) is the amount of adsorption corresponding to complete monolayer coverage and b (L/mg) is the Langmuir constant related to the energy or net enthalpy of adsorption. Kf and n are Freundlich constants related to adsorption capacity and adsorption intensity.
The essential features of the Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor or equilibrium parameter RL (equation (8)):
1 푅 = 퐸푞 (8) 퐿 (1 + 푏퐶표)
The value of RL indicates the adsorption process to be either unfavorable (RL > 1) or linear
(RL = 1) or favorable (0 < RL < 1) or irreversible (RL = 0). The Hg removal data obtained for the raw fique fiber was fitted to the two proposed model and the results are summarized in Table 5.3. 138 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 5.3. Langmuir and Freundlich isotherm models results for the Hg adsorption on raw fique fiber 29 pH [Hg]0 Fe Removal Langmuir Freundlich mg/L wt.% (%) 2 2 qm b RL R Kf n R 1 0 -1 24.4 0.13 123.82 0.0321 0.863 1.167 27.027 0.0026
From the data reported in Table 5.3, it can be interpreted that the predominant mechanism of mercury adsorption on the raw fique fiber approaches to a physisorption (described by
the fit of experimental data with Langmuir isotherm); from the RL factor can be concluded that the adsorption process on the raw fique fiber is a feasible operation. The Freundlich isotherm fitting was extremely poor.
Once the adsorption baseline experiment has been analyzed, a Box – Behnken design of experiment (DOE) was proposed in order to identify the effect of operating conditions on the Hg adsorption on the adsorbent material (iron nanoparticles on fique fiber), these experiments were performed on a random basis to minimize possible systematic errors that could generated. At the same time, the experimental conditions of each run and the percentages of removal achieved are described. The whole results of this experiment are presented in Annex 7; Table 5.4 shows the results of the DOE experiment adjusted to the Langmuir and the Freundlich isotherms.
Although some of the R2 fitting values for the Freundlich isotherms are relative good (above 0.90), 12 of the 15 “n” values calculated are negative which does not have any physical meaning, the 3 remaining “n” values are positive but their R2 fitting values are too small to considered the isotherm properly fitted. In conclusion, the Freundlich isotherm does not properly describe the Hg adsorption on the adsorbent material.
Table 5.4. Experimental levels used in the design of experiments Box - Behnken and values obtained for the Langmuir isotherm model and Langergren model of adsorption 30 Run pH [Hg]0 Fe Removal Langmuir Freundlich mg/L wt.% (%)
2 2 qm b RL R Kf N R 1 0 1 -1 71.73 84.75 -59 -0.001 0.988 107.72 -16.69 0.827 2 -1 0 -1 92.43 72.46 -345 -0.00003 0.998 78.31 125.00 0.006 3 0 -1 1 76.02 10.11 38.04 0.019 0.987 8.60 -3.88 0.036 4 -1 0 1 71.76 80.00 31.25 0.004 0.998 79.14 17.07 0.321 5 1 1 0 67.29 68.03 -1 -0.080 0.910 193.87 -2.58 0.862 5. Studies on adsorption mercury from aqueous solution on biocomposite material from fique fiber and iron nanoparticles 139
6 0 0 0 75.78 62.89 -53 -0.002 0.998 70.76 -42.37 0.385 7 1 0 1 51.44 42.02 1190 0.000 0.988 50.79 -9.22 0.123 8 0 -1 -1 86.32 11.21 223 0.003 0.996 11.45 26.38 0.566 9 1 -1 0 93.14 2.79 -6 -0.139 0.845 5.99 -2.67 0.351 10 0 1 1 74.44 227.27 15 0.004 0.998 249.34 -5.12 0.858 11 -1 1 0 71.73 172.41 -12 -0.005 0.997 205.97 -13.76 0.701 12 0 0 0 71.46 54.95 182 0.001 0.995 69.82 -2.20 0.942 13 1 0 -1 55.41 23.75 -35 -0.005 0.985 41.81 -15.80 0.166 14 0 0 0 71.58 57.80 16 0.008 0.994 41.81 192.31 0.002 15 -1 -1 0 39.09 2.54 -141 -0.013 0.976 4.11 63.69 0.010
In terms of the Langmuir isotherms, most of the R2 fitting values area above 0.90, however
2 8 of the RL values are negative which does not have any physical meaning. The other R values are relative small (below 0.019) meaning a close to irreversible adsorption, not a very common feature of physisorption type processes.
Under the fact that neither the Langmuir or Freundlich isotherms showed a good fitting for the experimental data of Hg adsorption on the adsorbent material and that the adsorbent material is made out of iron nanoparticles supported on modified fique fiber and could be chemically active, a pseudo-second-order kinetic model as Lagergren equation was proposed [24], Table 5.5, shows the differential and linearized form.
Table 5.5. Pseudo-second-order kinetic model of adsorption 31 Model (pseudo-second-order) Linealization form Langergren 푑푞(푡) 2 푡 1 1 = 푘2[푞푒 − 푞(푡)] (9) = 2 + 푡 (10) 푑푡 푞(푡) 푘2푞푒 푞푒
-1 -1 where k2 [g/mg min ] is the rate constant of pseudo-second-order model, qt (mg/g) is the
amount of adsorbed Hg on the adsorbent at time t and qe is the equilibrium sorption uptake (mg/g). The result of the data fitting from DOE with Lagergren model is summarized in Table 5.6.
Table 5.6. Experimental levels used in the design of experiments Box - Behnken and values obtained for the Lagergren Pseudo-second-order kinetic model 32 Run pH [Hg]0 Fe wt.% Removal (%) Lagergren
2 mg/L qe (mg/g) K2 (g/mg/min) R 1 0 1 -1 71.73 10.20 0.1396 0.997 140 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
2 -1 0 -1 92.43 14.82 0.0448 0.999 3 0 -1 1 76.02 -41.15 0.0009 0.987 4 -1 0 1 71.76 -8.98 0.1079 0.994 5 1 1 0 67.29 2.16 3.2460 0.975 6 0 0 0 75.78 21.19 0.0205 0.999 7 1 0 1 51.44 5.31 0.2397 0.996 8 0 -1 -1 86.32 11.47 26.385 0.566 9 1 -1 0 93.14 0.151 69.809 0.997 10 0 1 1 74.44 -151.52 0.0009 0.997 11 -1 1 0 71.73 22.272 0.0363 0.999 12 0 0 0 71.46 133.33 0.0005 0.999 13 1 0 -1 55.41 3.09 0.6374 0.999 14 0 0 0 71.58 96.1538 0.0009 0.996 15 -1 -1 0 39.09 0.1795 18.6474 0.987
The fitting results obtained for the pseudo-second-order kinetic model were very good, 14
2 of the 15 experiments shown R above 0.987. 12 of the 15 experiment present qe and K2 positive (with physical significance). This result indicates that the process of Hg adsorption on iron nanoparticles supported on modified fique fiber could be described as a chemisorption process, which would explain the odd behavior of the final removal of Hg as a function of adsorbent amount (Figure 5.2).
The equation of statistical adjustment coefficients second order (equation (11)) calculates the value of the final removal % based on the sample data of Table 5.6 where A:pH, B:
CHgo and C: Fe wt.%. 푟푒푚표푣푎푙 (%) = 488.122 − 18.0308A − 0.360682B − 51.5658C − 0.822002퐴2 2 2 + 0.0242588퐵 + 1.16096퐶 − 0.505189AB + 2.51977AC Eq + 0.239131BC (11)
The conditions under which the best percentage degradation (93.14%) was achieved was to: pH=10, mercury initial concentration = 1ppm and iron loading on the adsorbent(11) material 13.2 wt%. Table 5.7 shows the results of the statistical analysis model from equation (11), evaluated by ANOVA, this is evidence that pH factor is statistically significant with a confidence level of 95% (p> 0.05). Additionally, pH interactions with the 5. Studies on adsorption mercury from aqueous solution on biocomposite material from fique fiber and iron nanoparticles 141 other factors (initial concentration of mercury in solution and loading of iron nanoparticles), also are statistically significant, the efficiency obtained in the mercury removal, it is concluded that the levels analyzed were adequate.
Table 5.7. Analysis of variance (ANOVA) for qe (mg/g) by MiniTab 16 Statistical Software 33 Source DF Seq SS Adj SS Adj MS F P Regression 9 2503.63 2503.63 278.18 3.49 0.091 Linear 3 139.29 1305.80 435.27 5.46 0.049 A: pH 1 7.47 1138.40 1138.40 14.28 0.013
B: CHgo 1 9.87 127.2 127.20 1.60 0.262 C: %Fe 1 121.95 41.13 41.13 0.52 0.505 Square 3 251.67 259.69 86.56 1.09 0.435 AA 1 196.54 201.93 201.93 2.53 0.172 BB 1 20.24 17.58 17.58 0.22 0.658 CC 1 34.89 34.89 34.89 0.44 0.538 Interaction 3 2112.66 2112.66 704.22 8.83 0.019 AB 1 774.05 774.05 829.68 10.40 0.023 AC 1 1227.59 1227.59 1227.59 15.39 0.011 BC 1 111.02 111.02 111.02 1.39 0.291 Residual Error 5 398.70 398.70 79.74 Total 14 2902.33
An adjustment highly satisfactory between the calculated data and experimental data is reflected on the correlation coefficient values of R2 = 86.26% and R2 - adjust = 61.54%. Figure 5.4 shows how the model is very accurate to predict the removal percentage in the whole range of the studied variables. 142 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
100
80
60
40
20
Removal percentage (calc)percentage Removal 0 0 20 40 60 80 100 Removal percentage (exp) Figure 5.4. Experimental and calculated results of the experimental design for mercury removal. Responses considered removal % 47
In order to determine the appropriate fitting data regression and analysis of variance (ANOVA), analysis of residual plots that are defined as the difference between the set values (model) and the observed values (experimental) was performed. As shown in Figure 5.5a residues, follow a normal distribution, half of data takes positive values (over 50%) and the other half negative values (below 50%), which allows to conclude that there are no significant deviations of residuals from the normal distribution. Figure 5.5b, 5.5c and 5.5d allow to verify the homocedasticity of the residuals (constant variance) meaning they are symmetrically distributed and are not interdependent to each other. Residual Plots for Removal (%) a) Normal Probability Plot b) Versus Fits 99 10
90 5
l
t
a n
u 0
e
d c
50 i
r
s e
e -5 P b) b)R 10 -10
1 -10 0 10 50 60 70 80 90 Residual Fitted Value
Histogram Versus Order 4 10
5 y
3 l
c
a n
u 0
e
d
u i
2 s
q e
e -5
r
R F 1 -10
0 -10 -5 0 5 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Residual Observation Order Residual Plots for Removal (%) Normal Probability Plot Versus Fits 99 10
90 5
l
t
a n
u 0
e
d c
50 i
r
s e
e -5
P R 10 5. Studies on adsorption mercury from aqueous solution-10 on biocomposite material from 1 fique fiber and -10iron nanoparticles0 10 50 60 70 80 90 143 Residual Fitted Value c) d) Histogram Versus Order 10 4
5 y
3 l
c
a n
u 0
e
d i c) u d)
2 s
q e
e -5
r
R F 1 -10
0 -10 -5 0 5 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Residual Observation Order
Figure 5.5. Residual plots for qe a) Normal probability plot, b) Versus fits, c) Histogram and d) Versus order 48
In general, it is accepted that adsorption phenomena on lignocellulosic materials (like the raw fique fiber) is mainly governed by the physisorption mechanism through surface properties such as the presence of functional groups containing oxygen, proving to be an important factor in mercury adsorption [27]. Mercury adsorption in this type of surface has been described in terms of two fundamental driving forces. The first one is related to the mercury Lewis structures, which could bind to basic groups on the surface of the fique fiber. The second, is the affinity of the superficial functional groups to ionize when immersed in aqueous solution, allowing to the oxygen from the functional group to exchange charges with mercury [28]. However, the pH in which is located the solution is a factor that affects the ionization of the surface functional groups and disturbing the adsorption capacity because it directly affects the net balance of charges on the surface of the adsorbent material.
Models of physisorption isotherms and chemical kinetic models showed in Tables 5.4 and 5.6, allow to analyze that the main mechanisms of Hg on iron nanoparticles supported on modified fique fiber is mostly chemisorption (probably convolute with an small contribution from physisorption), several studies have reported important chemical and magnetic interactions of iron nanoparticle with mercury in adsorption processes, however most of them are reported for unsupported nanoparticles [25,26], some on supported nanoparticles [27,28], but none using fique fiber as supporting material.
In terms of the physical adsorption of Hg from aqueous solutions some Langmuir qm values have been reported: for activated carbon reported qm=10 mg/g [29], activated carbon of palm oil qm = 52.9 mg/g [30] and peanut hulls qm=109 mg/g [31], however not all the adsorption variables are comparable. 144 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Figure 5.6 shows that mercury adsorption is a process that depends largely on the pH, the greater adsorption is achieved at higher pH; it has been reported that increasing the pH improves the solubility of mercury species and promoting the effective contact between adsorbate molecules and adsorbent [32]. Hilson et al. [13], and Sreedhar, et al. [33], stated how the solution pH plays an important role in the adsorbent superficial functional groups by promoting their ionization, those ionized groups become focal point for adsorption. Therefore, the pHzpc value of the adsorbent material becomes an important property in the adsorption capacity; as it was determined in previous works the pHzpc value of the adsorbent material is 8.23. Subjecting the adsorbent material to a pH below
+ 8.23, the high concentration of hydronium ions (H3O ) in the solution will cause the material surface to charge positively, thereby hampering ion exchange with the metal ions Hg+2 and cations Fe+3 present in the nanoparticles.
When the pH of the solution increases above 8.23 the hydronium ion concentration decreases allowing the ionization the surface of fique fiber with iron nanoparticles anchored, increasing the adsorption of mercury and even generating exchange between charges Fe+3 and Hg+2 (chemisorption). In general, the adsorption efficiency of Hg (II) decreases with lowering pH, effect of pH is demonstrated in Figure 5.6 wherein the maximum adsorption at pH=10 and for solutions of pH 4 is observed and 5.7 removal performance was reduced. Contour Plot of Removal (%) vs pH. [Hg] 10 Removal (%) < 40 9 40 – 50 50 – 60 60 – 70 8 70 – 80 80 – 90 > 90
H 7 p
6
5
4 5 10 15 20 [Hg] (ppm) Figure 5.6. Contour plot of qe (mg/g) vs. pH and mercury initial concentration 49 5. Studies on adsorption mercury from aqueous solution on biocomposite material from fique fiber and iron nanoparticles 145 Contour Plot of Removal (%) vs %Fe. [Hg]
Removal 14,5 (%) < 40 40 – 50 14,0 50 – 60 60 – 70 13,5 70 – 80 80 – 90
> 90
% .
t 13,0
w
e F 12,5
12,0
11,5
11,0 5 10 15 20 [Hg] (ppm) Figure 5.7. Contour plot of qe (mg/g) vs. Fe wt% and mercury initial concentration 50
There is a direct relation between adsorption of mercury and the initial concentration of metal ions present in solution at low concentrations of mercury, the adsorption capacity of the adsorbent material is low, while increases by increasing the initial concentration, the above statement consistent with the results obtained in the present investigation shown in Figure 5.6. Other authors [21,34] have reported the same behavior, which is related to the fact that initially all the active sites on the surface of the fibers and fiber loaded with iron nanoparticles were vacant and the concentration gradient of metal ions is relatively high [35]. The extent of adsorption of ions decreases significantly with increasing contact time depending on the rate of reduction of vacant surface sites of the adsorbent material.
Conclusions The effects of the experimental conditions on the removal of Hg on raw and iron supported on modified fique fiber was studied. A Box-Behnken design of experiments allowed to determine the individual and the combined interaction of the main factor studied (pH, 퐶퐻푔0, and 퐹푒 %푤푡). A maximum Hg removal of removal of 93.14% was obtained operating at pH: 10, 퐶퐻푔0 : 1 푝푝푚, and 13.2 %퐹푒 푤푡. DOE results and the ANOVA analysis allow to conclude that the main factor in the operating conditions is pH; pH values above 8.23 benefit the removal process. Iron loading on the material adsorbent material was found to have a positive effect on adsorption. 146 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
The adjustment of the obtained experimental data to the different chosen model indicates that pseudo-second order chemical kinetic and Langmuir are the ones that better fit the experimental data, these were efficiently used to predict the adsorption of mercury on raw fique fibers and on iron nanoparticles supported on modified fique fiber; these models may indicate that main mechanism of adsorption on raw fique fiber is physisorption, meanwhile in the case of the iron nanoparticles supported on modified fique fiber the predominant mechanism is chemisorption.
According to the results obtained in this research, it was confirmed that fique fiber and iron nanoparticles present a high potential for removing Hg (II) from synthetic water due to the presence of hydroxyl and carbonyl groups in the surface of biomasses, which has great affinity to metal ions.
The results obtained could be applied to remove mercury from waste water using an organic material loaded with iron nanoparticles. Proved to be a promising solution because the combination of properties provided by each of the elements of the adsorbent material. The effects of functional groups on the adsorbent material surface may have a significant effect on mercury adsorption. Increasing sequestration capacity of Hg may also be enhanced by chemical and magnetic properties reported for iron nanoparticles.
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150 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Conclusions and recommendations
The principal achievements within this master thesis are:
1) Chemical and physical improvements due to pretreatment and functionalization were observed in the raw fique, among the enhanced physical characteristics are: reduced crystal size, homogeneous fique surface by ultrasound pretreatment and increased surface area. In term of the chemical changes obtained on the treated fiber is worth to mention, exposure and activation of functional groups, cationization of the fiber surface with chemically active Na+ cations. 2) The synthesis of composite material made out of modified fique fiber and iron nanoparticles, was successfully achieved, concluding that functionalized fiber has better characteristics to exchanges iron species with the impregnating solutions that the raw fiber; it can be concluded that the cationized sites interact with iron specie to create well dispersed nanoparticles, that evolved to form aggregates. Crystallographic analyses show mainly the presence of iron oxide species, along with some iron zero valent, which haven reported to be chemically active for oxidation process and is in agreement with Orange II oxidation experiments performed.
3) The composite material from fique and iron nanoparticles, is a material with great potential to be carried on an industrial scale, because of the easy synthesis methodology and the low costs involved in their preparation.
4) Orange II degradation experiment showed the catalyst to be an excellent material to degrade the azo group in the Orange II molecule and therefore reducing the color of the contaminated water. In term of mineralization only partial mineralization was obtained, implying that remaining intermediates such as benzene,
+ -3 naphthalene, NH4 , NO and other intermediaries could persists. A simplified pseudo-first-order kinetic model was proposed and was able to describe 16 of the degradation conditions with a R2 above 0.9; a very remarkable result for such a simple model. Conclusions and recommendation 151
5) From the operating conditions analyzed in the degradation of dye OII, the synthesized catalyst shows remarkable catalytic activity at low pH, feature that has not been reported for other catalyst in these type of reaction. It turns this catalyst into a great choice to treat contaminated effluents with very acidic conditions (pH = 2.5), pH where the best value of degradation percentages were achieved
6) Mercury removal demonstrated very interesting results as the predominant mechanism was the chemical adsorption, as determined by adjusting a kinetic model of pseudo-second-order, which makes the removal process more efficient, this can be attributed the combination of properties of the support and the iron nanoparticles.
In order to continue this study, are proposed as recommendations:
+3 1) At the time of synthesis of nanoparticles in Chapter 3 the molar ratio 2:1 (BH4ˉ / Fe ) were maintained, there are different reports in which the ratio reducing agent / agent precursor allows for different properties in the characteristics of nanoparticles, so would be ideal an evaluation on the variation of the relationship to see which the best condition is. It is also important to explore new alternative synthesis of nanoparticles, in order to obtain for example nano zero valent iron (nZVI), a type of nanoparticles with properties that further accelerate the oxidation process.
2) From the treated wastewater it is important to identify the possible intermediaries produced as a result of mineralization of the dye OII, which would in turn important information when the challenge of proposing a reaction mechanism arises, this reaction mechanism will be also of great support in the derivation of a complete kinetics equation necessary to perform any scaling process and real application.
3) The analysis regarding the removal of mercury opens a new an interesting study, which is, the removal of Mercury via highly selective chemisorption processes. Among the recommendations made regarding the removal of mercury, it should be noted that when using a synthetic water mercury is mainly found in its ionic form (Hg+2), however, in real waters mercury may not necessary be in this form, creating complexes and interacting with other materials in the contaminated water. 152 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
4) It is appropriate to assess the regeneration of the adsorbent material of Fique fiber and iron nanoparticles, through the study of the magnetic properties of iron nanoparticles to improve its economic viability, so its future is not just limited to laboratory scale but also applicable to industrial scale.
Finally, it is open to continue exploring new alternatives for wastewater treatment base in the biomaterial synthesized in this thesis, for example photocatalysis and testing the catalyst with other pollutants molecules and elements (dyes with other structures, other heavy metals, phenols, hormones and even pesticides).
Wastewater treatment using an iron nanocatalyst supported on Fique fibers 153
Annex Annex 1 Table 1. Nitrogen adsorption isotherm for raw fique fiber P/Po Volume [cc/g] STP 0.01325 0.07197 0.04348 0.10496 0.07503 0.13275 0.10729 0.15346 0.13951 0.16688 0.16927 0.18645 0.20508 0.20301 0.23525 0.21357 0.26831 0.22607 0.29779 0.23757 0.33395 0.25094 3.65E-01 0.26311 3.97E-01 0.27485 4.29E-01 0.28432 4.62E-01 0.29752 4.94E-01 0.31146 5.26E-01 0.32402 5.58E-01 0.33815 5.91E-01 0.34821 6.23E-01 0.36182 6.56E-01 0.3763 6.87E-01 0.3923 7.20E-01 0.41023 7.44E-01 0.42487 8.58E-01 0.49995 8.90E-01 0.52553 9.22E-01 0.55137 9.49E-01 0.58178 9.73E-01 0.64644 9.85E-01 0.68558 9.88E-01 0.71607 9.90E-01 0.73601 154 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 2. Nitrogen adsorption isotherm for pretreated fique fiber (M30)
P/Po Volume [cc/g] STP 0.01901 0.08765 0.04501 0.19796 0.08523 0.28448 0.11752 0.33696 0.14992 0.37174 0.18313 0.39136 0.21503 0.42354 0.2473 0.44594 0.27963 0.45497 0.31124 0.48343 0.34343 0.51236 3.77E-01 0.52075 4.09E-01 0.53072 4.41E-01 0.54034 4.74E-01 0.54668 5.06E-01 0.55426 5.39E-01 0.55997 5.71E-01 0.56748 6.03E-01 0.57578 6.35E-01 0.58425 6.67E-01 0.59483 7.00E-01 0.60247 7.32E-01 0.61032 7.64E-01 0.6169 7.97E-01 0.62624 8.29E-01 0.63983 8.61E-01 0.65467 8.93E-01 0.66947 9.25E-01 0.69289 9.56E-01 0.72392 9.67E-01 0.76199 9.74E-01 0.79767 9.82E-01 0.84129 9.89E-01 0.88087 9.90E-01 0.92201
Wastewater treatment using an iron nanocatalyst supported on Fique fibers 155
Table 3. Nitrogen adsorption isotherm pore pretreated fique fiber (M60)
P/Po Volume [cc/g] STP 0.00382 0.07701 0.00847 0.14001 0.02111 0.22501 0.04369 0.34301 0.0745 0.45001 0.08781 0.52001 0.10868 0.58601 0.15701 0.74001 0.218 0.82901 0.25344 0.87001 0.29591 0.89501 3.42E-01 0.93901 3.75E-01 0.96001 4.08E-01 0.96001 4.45E-01 0.96001 4.84E-01 0.96801 5.21E-01 0.99201 5.71E-01 1.00801 6.31E-01 1.03201 6.63E-01 1.04001 7.03E-01 1.07101 7.45E-01 1.09501 7.79E-01 1.12701 8.12E-01 1.15901 8.56E-01 1.21401 8.90E-01 1.25401 9.20E-01 1.30001 9.40E-01 1.33301 9.49E-01 1.36501 9.60E-01 1.43701 9.78E-01 1.54001 9.89E-01 1.67501 9.96E-01 2.15901
156 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 4. Nitrogen adsorption isotherm for pretreated fique fiber (M90)
P/Po Volume [cc/g] STP 0.00779 0.04701 0.03601 0.16301 0.08609 0.32001 0.12455 0.40001 0.16236 0.47401 0.20117 0.51601 0.23666 0.58001 0.26111 0.60801 0.30965 0.69501 0.34331 0.73701 0.37826 0.77701 4.11E-01 0.79601 4.44E-01 0.80801 4.75E-01 0.83001 5.03E-01 0.83801 5.43E-01 0.84501 5.75E-01 0.85701 6.27E-01 0.86801 6.45E-01 0.88301 6.94E-01 0.90201 7.38E-01 0.91301 7.83E-01 0.94701 8.22E-01 0.96001 8.66E-01 1.00401 8.96E-01 1.05301 9.20E-01 1.09101 9.40E-01 1.13201 9.56E-01 1.15501 9.68E-01 1.22301 9.74E-01 1.26901 9.78E-01 1.33976 9.82E-01 1.43609 9.87E-01 1.53701 9.93E-01 1.79601
Wastewater treatment using an iron nanocatalyst supported on Fique fibers 157
Table 5. Nitrogen adsorption isotherm for fuctionalizated fique fiber (MC1)
P/Po Volume [cc/g] STP 0.01603 0.08012 0.03801 0.17602 0.06002 0.26901 0.08421 0.36003 0.11604 0.46015 0.15167 0.56001 0.19405 0.66403 0.23365 0.72001 0.27815 0.77403 0.30626 0.81201 0.35005 0.83191 0.38495 0.83191 0.43555 0.85475 0.45803 0.86616 0.51425 0.90042 0.53673 0.90042 0.59857 0.92326 0.62667 0.93467 0.68851 0.96893 0.71661 0.98202 0.77845 1.01461 0.82389 1.02602 0.87401 1.06028 0.89651 1.08026 0.94756 1.16304 0.96958 1.24297 0.97722 1.33801 0.98401 1.44405 0.98925 1.59203 0.99206 1.68306 0.99872 1.92301
158 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 6. Nitrogen adsorption isotherm for fuctionalizated fique fiber (MC2)
P/Po Volume [cc/g] STP 0.02302 0.11601 0.04805 0.22001 0.07201 0.29604 0.09802 0.38403 0.12778 0.47601 0.15776 0.54003 0.19731 0.64601 0.23927 0.71304 0.27401 0.78004 0.31188 0.82901 0.35186 0.87304 0.39058 0.87003 0.44117 0.85803 0.46365 0.86401 0.51425 0.87405 0.53673 0.87803 0.59857 0.89501 0.63229 0.90207 0.68711 0.92897 0.72901 0.94901 0.77845 0.99405 0.82904 1.03744 0.87963 1.09453 0.90212 1.11737 0.93001 1.17446 0.95403 1.23503 0.96705 1.30302 0.97942 1.40506 0.98628 1.50708 0.99075 1.59804 0.99507 1.67703 0.99861 1.77309
Wastewater treatment using an iron nanocatalyst supported on Fique fibers 159
Table 7. Nitrogen adsorption isotherm for fuctionalizated fique fiber (MC3)
P/Po Volume [cc/g] STP 0.02285 0.20006 0.04601 0.29609 0.07302 0.38436 0.10603 0.49415 0.14604 0.63119 0.18305 0.72422 0.21638 0.78824 0.25408 0.83125 0.30309 0.85126 0.37382 0.88827 0.42443 0.90108 0.45514 0.90527 0.49753 0.92028 0.52565 0.93672 0.58188 0.94859 0.60999 0.96047 0.67185 0.97235 0.69996 0.99017 0.76181 1.02631 0.78993 1.05551 0.86303 1.09114 0.88552 1.12678 0.92911 1.18135 0.95862 1.26038 0.97719 1.33841 0.98229 1.39042 0.98814 1.44043 0.98955 1.46544 0.99943 1.61048
160 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Annex 2 Table 1. Nitrogen adsorption isotherm for 1 day of impregnation
P/Po Volume [cc/g] STP 0.02901 0.12004 0.05602 0.23007 0.08202 0.32411 0.11603 0.42013 0.15605 0.52016 0.19706 0.60918 0.24607 0.70821 0.29509 0.77423 0.33705 0.81224 0.3892 0.826 0.44131 0.822 0.4872 0.82311 0.52002 0.83395 0.57625 0.86652 0.60437 0.85837 0.65021 0.87193 0.69434 0.89906 0.74422 0.92828 0.78431 0.94246 0.85741 0.98586 0.87991 1.00214 0.91327 1.08352 0.95159 1.22237 0.98392 1.57182 0.98505 1.58047 0.98955 1.66951 0.99092 1.68751 0.99517 1.73152 0.99879 1.82755
Wastewater treatment using an iron nanocatalyst supported on Fique fibers 161
Table 2. Nitrogen adsorption isotherm for 2 days of impregnation
P/Po Volume [cc/g] STP 0.02401 0.12604 0.05502 0.26908 0.08603 0.40012 0.11804 0.50515 0.14904 0.58017 0.18406 0.66421 0.22507 0.74622 0.26108 0.78524 0.30072 0.80724 0.33133 0.83425 0.37945 0.82525 0.42443 0.82645 0.45255 0.84225 0.50315 0.86357 0.52565 0.86071 0.58751 0.91211 0.61561 0.92353 0.67747 0.95782 0.70558 0.95209 0.76744 0.98064 0.78993 1.0033 0.86865 1.08344 0.89114 1.10628 0.93613 1.15235 0.96471 1.22051 0.98392 1.46744 0.98674 1.63949 0.98955 1.65453 0.99236 1.74452 0.99517 1.75453 0.9966 1.76253 0.99732 1.78253 0.99924 1.92758
162 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Table 3. Nitrogen adsorption isotherm for 3 days of impregnation
P/Po Volume [cc/g] STP 0.01901 0.09101 0.07101 0.29103 0.11207 0.42001 0.15773 0.53202 0.19305 0.61503 0.22756 0.68601 0.27112 0.78504 0.30063 0.82301 0.35685 0.88002 0.42993 0.89001 0.45241 0.88502 0.50862 0.88502 0.53111 0.89001 0.59341 0.89301 0.62152 0.89302 0.66101 0.90001 0.71099 0.91102 0.7733 0.93611 0.79531 0.95212 0.86839 0.99868 0.89088 1.02335 0.94006 1.08364 0.96395 1.24634 0.98152 1.45907 0.98644 1.55447 0.98925 1.60612 0.99066 1.64309 0.99487 1.79435 0.99682 1.87312 0.99851 1.99301 0.99909 2.09201
Wastewater treatment using an iron nanocatalyst supported on Fique fibers 163
Annex 3
Figure 1. Wavelength with maximum absorption for the OII dye
Figure 2. Calibration curve of OII at 486nm using UV-Vis spectrophotometry
164 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Annex 4 Table 1. Factors evaluated in the dye degradation of OII using iron supported on fique catalyst 34 Level Factor Low Medium High pH 2.5 3 3.5 [OII]o (M) 2푥10−5 1.1푥10−4 2푥10−4 −4 −3 −2 [H2O2]o (M) 1푥10 5.05푥10 1푥10 Fe wt.% 10.9 13.2 14.9 Table 2. Experiments values of Box - Behnken experimental design, degradation percentage and kap obtained for each experimental conditions 35 Run pH COIIo (M) H2O2 (M) Fe wt.% %Deg 1 0 -1 1 0 5.91 2 0 0 0 0 6.83 3 -1 0 0 1 81.94 4 1 0 0 -1 19.67 5 1 0 0 1 1.22 6 0 1 -1 0 1.28 7 0 1 1 0 0.56 8 -1 0 0 -1 93.23 9 0 -1 -1 0 53.30 10 1 1 0 0 0.23 11 -1 -1 0 0 94.50 12 -1 1 0 0 62.96 13 0 0 0 0 27.98 14 1 -1 0 0 5.43 15 0 0 1 -1 60.19 16 0 0 -1 1 4.31 17 0 0 1 1 3.49 18 0 0 -1 -1 40.31 19 0 -1 0 1 49.05 20 1 0 1 0 4.23 21 0 1 0 1 0.30 22 0 0 0 0 20.08 23 -1 0 -1 0 86.72 24 1 0 -1 0 20.27 25 -1 0 1 0 95.61 26 0 1 0 -1 2.24 27 0 -1 -1 -1 7.28 Wastewater treatment using an iron nanocatalyst supported on Fique fibers 165
Figure 1. Data Experiments values of Box - Behnken experimental design, degradation percentage 51
Figure 2. Data Experiments values of Box - Behnken experimental design, degradation percentage 52 166 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Annex 5
Figure 1. Experimental maximum degradation value of OII degradation
Wastewater treatment using an iron nanocatalyst supported on Fique fibers 167
Annex 6
Figure 1. Calibration curve of Fe using FAAS
Table 1. Data obtained for Fe by FASS
Run Abs [Fe] ppm Run Abs [Fe] ppm 1 0.005 0.355 15 0.009 0.740 2 0.006 0.451 16 0.005 0.355 3 0.012 1.028 17 0.005 0.355 4 0.002 0.067 18 0.007 0.548 5 0.006 0.451 19 0.013 1.124 6 0.005 0.355 20 0.005 0.355 7 0.004 0.259 21 0.006 0.451 8 0.029 2.661 22 0.009 0.740 9 0.006 0.451 23 0.024 2.181 10 0.005 0.355 24 0.005 0.355 11 0.022 1.988 25 0.029 2.661 12 0.026 2.373 26 0.005 0.355 13 0.006 0.451 27 0.004 0.259 14 0.006 0.451 Average 0.00985 0.822
168 Wastewater treatment using an iron nanocatalyst supported on Fique fibers
Annex 7 Table 1. Factors assessed in mercury removal using a adsorbent from Fique and iron nanoparticles36 Level Factor Low Medium High pH 4 7 10 [Hg]o (ppm) 1 10 14 Fe wt.% 10.9 13.2 14.9
Table 2. Experimental levels used in the design of experiments Box - Behnken and values obtained for the Langmuir isotherm model and Langergren model of adsorption 37. Run pH [Hg]0 Fe Removal mg/L wt.% (%)
1 0 1 -1 71.73 2 -1 0 -1 92.43 3 0 -1 1 76.02 4 -1 0 1 71.76 5 1 1 0 67.29 6 0 0 0 75.78 7 1 0 1 51.44 8 0 -1 -1 86.32 9 1 -1 0 93.14 10 0 1 1 74.44 11 -1 1 0 71.73 12 0 0 0 71.46 13 1 0 -1 55.41 14 0 0 0 71.58 15 -1 -1 0 39.09
Wastewater treatment using an iron nanocatalyst supported on Fique fibers 169
Figure 1. Data Experiments values of Box - Behnken experimental design, removal percentage 53
Figure 2. Data Experiments values of Box - Behnken experimental design, removal
percentage 54