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Decoration of Graphene Oxide with Silver Nanoparticles And DECORATION OF GRAPHENE OXIDE WITH SILVER NANOPARTICLES AND CONTROLLING THE SILVER NANOPARTICLE LOADING ON GRAPHENE OXIDE Thesis Submitted to The School of Engineering of the UNIVERSITY OF DAYTON In Partial Fulfillment of the Requirements for The Degree Master of Science in Chemical Engineering By Venroy G. Watson UNIVERSITY OF DAYTON Dayton, Ohio May, 2014 DECORATION OF GRAPHENE OXIDE WITH SILVER NANOPARTICLES AND CONTROLLING THE SILVER NANOPARTICLE LOADING ON GRAPHENE OXIDE Name: Watson, Venroy G. APPROVED BY: _______________________ _______________________ Elena A. Guliants, Ph.D. K. A. Shiral Fernando, Ph.D. Associate Professor Senior Research Scientist Electrical Engineering UDRI Advisory committee Chairperson Research Advisor _______________________ _______________________ Amy Ciric, Ph.D. Alexander B. Morgan, Ph.D. Group Leader and Distinguished Senior Lecturer Research Scientist Chemical Engineering Committee Member UDRI Committee Member _______________________ _______________________ John G. Weber, Ph.D. Tony E. Saliba, Ph.D. Associate Dean Dean, School of Engineering School of Engineering & Wilke Distinguished Professor ii ABSTRACT DECORATION OF GRAPHENE OXIDE WITH SILVER NANOPARTICLES AND CONTROLLING THE SILVER NANOPARTICLE LOADING ON GRAPHENE OXIDE Name: Watson, Venroy G. University of Dayton Research Advisor: Dr. K.A. Shiral Fernando Committee Chair: Dr. Elena A. Guliants Academic Advisor: Dr. Kevin J. Myers Metal-decorated carbon substrates such as carbon nanotubes, graphene oxide (GO), and carbon nanoparticles have been of great interest to the scientific community for the last three decades due to numerous potential applications. Graphene oxide is an oxidized derivative of graphene and is obtained from the severe oxidation of graphite powder. This process introduces oxygen-containing functional groups to the surface of GO. Chemical species both organic and inorganic molecules can be attached to the surface of graphene oxide via these functional groups. Also, functional groups on its surface can serve as nucleation and growth sites for metalnanoparticles. Metal nanoparticles especially Ag, have exhibited remarkable optical, antibacterial, and imaging properties just to name a few, at the nanometer level. iii However, during synthesis, these nanoparticles tend to agglomerate resulting in loss of their nanoscale properties. Since GO high surface area can serve as nucleation sites for metal nanoparticles, it can be used as a substrate to deposit metal nanoparticles. This will reduce agglomeration of Ag nanoparticles, thus allowing the properties that Ag exhibit at the nano-level to be accessed. In addition, recent results show that Ag-GO has very good antibacterial results. GO traps bacteria while Ag kills bacteria. Therefore, we intend to obtain the optimum ratio of Ag to GO which can be used in future studies in antibacterial filters. In this work, synthesis and characterization of Ag-decorated GO was investigated using sonochemistry. The initial approach to control the loading of Ag nanoparticle on the su rface of GO involved changing the weight ratio between silver acetate and GO. However, it failed to achieve the desired control of Ag loading on GO surface and has led to the second approach, in which 26 wt% Ag-GO sample (26 wt% Ag) was mixed with GO. TEM analysis showed the second approach offers a better control of silver loading on GO surface. 26 wt% Ag-GO sample was prepared by mixing GO with silver acetate in DMF and sonicated for 20 minutes. By varying the weight ratio between 26 wt% Ag-GO and GO, a series of Ag-GO samples with different Ag loadings (15 6to wt% Ag) were synthesized and studied using TEM, XRD, TGA and DSC. Resulting Ag nanoparticles were spherical in shape with an average size of ~6-7 nm, a size distribution of 1-22 nm, and were evenly distributed on the surface of GO sheets. In XRD, all the Ag-decorated GO samples exhibited the characteristic peaks of GO and fcc Ag. Thermal analysis performed for all Ag-GO samples using simultaneous TGA/DSC measurement revealed that the peak related to the combustion of graphitic carbon shifted to lower temperatures after GO was decorated with Ag nanoparticles. iv The analysis of Ag-GO samples with different Ag loadings, especially TEM analysis revealed that the newly added GO is also homogeneously decorated with Ag nanoparticles. This means Ag nanoparticles should migrate from 26 wt% Ag-GO to newly-added GO without any coalescence of Ag nanoparticles. Since the newly added GO has the same morphology as GO of 26 wt% Ag-GO, it is difficult to confirm the migration of Ag nanop articles from Ag-GO to newly-added GO. For this purpose, multi-walled carbon nanotube (MWNTs) was mixed in DMF with 26 wt% Ag-GO instead of GO because MWNTs have very different morphology from GO. Resulting Ag-GO-MWNTs product consistently demonstrated that MWNTs were evenly decorated with Ag nanoparticles and XRD analysis confirmed the presence of fcc silver nanoparticles in the sample. This control experiment confirmed that Ag nanoparticles are migrating from GO to newly-added MWNTs without any coalescence. In addition, little or no migration of Ag nanoparticles was observed in other solvents, including water and hexane. In addition, our further experiments showed that Ag nanoparticles did not migrate from Ag-GO to neither carbon nanoparticles nor cotton wool even though these materials possess similar functional groups. v ACKNOWLEDGEMENTS I would like to give God thanks for his mercies and blessings which have helped me to reach this stage in my life. God, I am exceedingly thankful to you. I would like to thank my very loving and supportive family for their support and motivation over the years. Their encouragements and warm words of advice have been very instrumental in my life. I would like to give Special thanks to Dr. Christopher Bunker, Dr. William Lewis and Dr. Elena Guliants, for their leadership roles. Dr. Bunker, I am especially thankful to you for pushing me to extreme lengths scientifically, I know you did it in order for me to become a better researcher. Dr. Guliants, you have been very supportive and encouraging over the years. I am very appreciative of your help. Thanks to Dr. Lewis for his positive recommendations. I would like to give special thanks to my advisor, Dr. Shiral Fernando, who continuously trained me to become a better researcher. He was more than a research advisor; he is like a brother to me. He is always looking out for my best interest. His guidance and patience have led to my success in this group. Today, I can proudly say he has impacted my life significantly in a positive way and I am very thankful. vi I would like to thank Dr. Kevin Myers for his support in academic decisions. I would also like to thank every member of this research group for their assistance over the years, especially Marcus Smith for well needed XRD work and Barbara Miller for TEM work. I would like to thank my friends and classmates who have helped me during my time at the University of Dayton. I would also like to thank Dr. Amy Ciric and Dr. Alexander Morgan for serving on my committee. I appreciate your time and wisdom. vii TABLE OF CONTENTS ABSTRACT….………………………….………………………………..…………….iii ACKNOWLEDGEMENTS…………………………………….…...……...……………vi TABLE OF CONTENTS…..………………………………………..…….……………viii LIST OF FIGURES………..…………………………………………………………..…xi LIST OF TABLES………..…………………………………….……………..………..xvi CHAPTER 1: INTRODUCTION……………………...…………………..…….……….1 1.1 Synthesis methods of graphene……..………...……………….……….….…...……..6 1.2 Graphene oxide..……………………………………………….……….…….…...…..8 1.3 Structure of graphene oxide….…………………………….………………...….…..11 1.4 Graphene oxide chemical reactivity and solubility…………………………...….…..15 1.5 Reduction of graphene oxide………..………………….…….……….…..….……...18 1.5.1 Chemical reduction of graphene oxide……...…....…………...19 1.5.2 Thermal reduction of graphene oxide……...…..………………23 1.5.3 Electrochemical reduction of graphene oxide ……….…….…..24 1.6 Silver (Ag) nanoparticle………..…………………..…………………..…………...26 1.7 Stabilized and solvent soluble metal nanoparticle synthesis……………..…………28 1.8 Templated synthesis of noble metal nanoparticles………...…………….…….……31 1.9 Graphene oxide as template for metal nanoparticle synthesis……..…………..……31 1.9.1 Thermal method………...………..……………………….….…32 . viii 1.9.2 Photochemical method……..………………………………….35 1.9.3 Chemical reduction method……..…………………………….39 1.9.4 Microwave-assisted method…..………………………………..42 1.9.5 Sonochemical decoration of graphene oxide and other carbon substrates.....................................................................................45 1.10 Sonochemistry……..……………….….....………………..…………………….….50 1.11 Migration of metal nanoparticles between carbon substrates…………..…………..55 CHAPTER 2: EXPERIMENTAL METHODS…….………….…….…………….…….57 2.1 Materials…..…………………………………………..……………………….……..57 2.2 Sonochemical synthesis of Ag nanoparticles……...………………………..….…….57 2.3 Synthesis of graphene oxide…………..…………………….………………………..58 2.4 Acid treatment of MWNTs…………………..……………….……………...………59 2.5 Acid treatment of CNPs…………………..………………………….……..…..……59 2.6 Synthesis of peglated carbon nanoparticles (CNP-PEG)…………..……..….………60 2.7 Sonochemical synthesis of Ag-GO with 26 wt% Ao g l ading………………………..60 2.8 Synthesis of Ag-GO with 15 wt% and 10 wt% by changing Ag silver acetate ratio.............................................................................................................................61 2.9 Synthesis of 15 wt% Ag-GO sample by changing the ratio of 26 wt% Ag-GO to GO……….…………………………………..…...………..…………........……..….61
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