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© Copyright by Hang Ngoc Nguyen 2017 All Rights Reserved GRAPHENE AND GRAPHENE OXIDE TOXICITY AND IMPACT TO ENVIRONMENTAL MICROORGANISMS A Dissertation Presented To the Faculty of the Department of Civil and Environmental Engineering University of Houston In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in Environmental Engineering by Hang Ngoc Nguyen August 2017 GRAPHENE AND GRAPHENE OXIDE TOXICITY AND THE IMPACT TO ENVIRONMENTAL MICROORGANISMS _________________________________ Hang Ngoc Nguyen Approved: __________________________________________ Chair of Committee Debora F. Rodrigues, Associate Professor, Civil and Environmental Engineering University of Houston Committee Members: __________________________________________ Yandi Hu, Assistant Professor, Civil and Environmental Engineering University of Houston __________________________________________ Stacey Louie, Assistant Professor, Civil and Environmental Engineering University of Houston __________________________________________ Francisco C. Robles Hernandez, Associate Professor Department of Engineering Technology College of Technology Building University of Houston __________________________________________ Sarah L. Wallace, Aerospace Technologist, Life Science Research National Aeronautics Space Administration NASA Johnson Space Center, Houston __________________________________________ Megan L. Robertson, Assistant Professor Chemical and Biomolecular Engineering University of Houston ___________________________ _________________________________________ Suresh K. Khator, Associate Dean Roberto Ballarini, Department Chair Cullen College of Engineering Civil and Environmental Engineering Acknowledgements First of all, I am extremely grateful to my advisor, Dr. Debora F. Rodrigues, for her guidance, useful discussions, and brainstorming sessions, especially during difficult conceptual development stages of my Ph.D. work. Her deep insights helped me at various stages of my studies and experiments. I also remain in debt for her understanding and supporting during the times when I was really depressed or distracted due to personal problems. The skills and knowledge I acquired during my doctoral studies certainly made me a better researcher and future educator. I also would like to especially thank her for always trusting me and being supportive and patient with me. I will carry all teachings and knowledge I was able to obtain through her advising during my doctoral studies to the next steps in my career. She has always trusted and supported me unconditionally. I am thankful for having her as my advisor in my Ph.D. journey. She made my time at the University of Houston more than just an educational experience, but also an adventure to make me become a better person and future role model for female scientists. I am also grateful to my thesis committee for taking the time to give me constructive and valuable suggestions on my research project to enhance its quality and impact. I also would like to extend my gratitude to my laboratory group mates who always supported me during my work in the laboratory. Special thanks to: Dr. Catherine M. Santos, Dr. Charisma Lattao, Dr. Enrico Nadres, Dr. Felipe Ferrera, and Dr. Tugba Onal Okay who were always helpful and supportive in many different ways. Our research group has been a source of friendship as well as an excellent environment for interaction and collaboration. I want to take a chance to thank all my collaborators, especially Dr. Sarah L. Wallace, Dr. Clemencia Chaves Lopez, and Dr. Rodrigo Cardoso Oliveira, which I worked extensively during my journey at UH. v I also would like to thank all UH staff member who helped me academically and personally. I specially acknowledge the financial support from the National Science Foundation Career Award (NSF Award # 1150255) for supporting me in my research. I also extend my thanks to the authority of Sims South Bayou Treatment Plant for providing wastewater samples used in my studies. Additionally, I would like to send a special thanks to Dr. Alison M McDermott, College of Optometry at UH, for permitting me to use her laboratory and get help from her senior assistant at the human culture laboratory. I would like to thank my family (my Mom, Dad, sister, brother-in-law, and all relatives) for their unconditional love and support during my education even though we are far apart from each other. Special thanks to my uncle and aunt who brought me to the United States to get a better life and without whom I would not have been able to start my educational journey in US. I would like to acknowledge the most important person in my life – my husband Jimmy. He has been a constant source of strength to me. There were times during the past five years when everything seemed hopeless due to problems in my research project and family health issues. Although he did not know what and how to help me, he constantly encouraged me and was always by my side. Finally, I wish to express my sincere appreciation to those who have contributed to this work and supported me in one way or the other during my amazing journey. Hang Ngoc Nguyen University of Houston August 2017 vi GRAPHENE AND GRAPHENE OXIDE TOXICITY AND THE IMPACT TO ENVIRONMENTAL MICROORGANISMS An Abstract of a Dissertation Presented To the Faculty of the Department of Civil and Environmental Engineering University of Houston In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in Environmental Engineering by Hang Ngoc Nguyen August 2017 vii Abstract In natural and engineered environments, such as landfills and wastewater treatment plants, microorganisms are responsible for cleaning the environment by digesting and biodegrading contaminants. Antimicrobial pollutants can seriously hinder the functionality of native microbial populations leading to ineffective removals of biological and chemical wastes. Additionally, microorganisms can have deleterious effects to society through diseases and food spoilage. Therefore, it is essential to understand the effect of these nanomaterials on microbial populations as well as their role in hindering microbial activities, such as biological wastewater treatment and antimicrobial properties, to keep the environment balanced and to develop safe antimicrobial applications. This study presents the effects of graphene (G) and graphene oxide (GO) to fungi and bacteria to identify their impact to the environment and antimicrobial properties for potential applications. These nanomaterials were shown to inhibit significantly fungal growth and their mechanisms of inactivation involved apoptosis of the fungal hyphae. Acute and chronic toxicity to bacterial communities was also investigated in wastewater. The presence of high concentrations of these nanomaterials in the acute assays affected the carbon, nitrogen and phosphorus biogeochemical cycles significantly. While the chronic assay, showed that the bacterial population shifted differently in the presence of G or GO. Overall, GO was shown to have a more pronounced toxicity than G to the microbial communities in activated sludge. The antimicrobial properties of these nanomaterials were further explored for application as antimicrobial coatings with polymeric adhesives. The coatings with polymeric adhesives were effective against a wide range of bacteria and did not present cytotoxicity to human corneal epithelial cells, which implied these coatings are promising for biomedical applications. viii Table of Contents Acknowledgements ......................................................................................................................... v Abstract ..........................................................................................................................................viii Table of Contents ............................................................................................................................ ix List of Figures ................................................................................................................................. xiii List of Tables ................................................................................................................................ xviii List of abbreviations used in the thesis ......................................................................................... xix CHAPTER 1 RESEARCH HYPOTHESIS AND LITERATURE REVIEW ......................................... 1 1.1 RATIONALE AND HYPOTHESES DEVELOPMENT .......................................................... 1 1.2 GRAPHENE–BASED NANOPARTICLES ............................................................................ 4 1.3 SYNTHESIS METHODS OF G AND GO ............................................................................ 5 1.4 ANTIMICROBIAL PROPERTIES OF GRAPHENE – BASED NANOPARTICLES ..................... 7 1.4.1 Graphene ........................................................................................................... 7 1.4.2 Graphene oxide ................................................................................................. 8 1.4.3 Graphene polymer nanocomposites ............................................................... 10 1.4.4 Physicochemical properties of graphene – based nanoparticles that dictate the biological activity ................................................................................................ 12 1.5 MECHANISMS OF ANTIMICROBIAL ACTIVITY ............................................................