Electrospun nanofibrous bismuth based materials for photocatalytic applications

Electrospun Nanofibrous Bismuth-based Materials for Photocatalytic Applications Bhavatharini Ram Suganya Rajaraman B Eng , (Mechanical Engineering) A Thesis submitted for the Degree of Master of Engineering Department of Mechanical Engineering National University of Singapore 2013 Decl aration I hereby declare that this thesis is my original work and it has been written by me in its entirety I have duly acknowledged all the sources of information which have been used in the thesis This thesis has also not been submitted for any degree in any university previously Bhavatharini Ram Suganya Rajaraman 20 January 2013 i Acknowledgements Many people have contributed either directly or indirectly to this study First and foremost, I would like to express my deepest gratitude and debt to my research supervisor, Prof Seeram Ramakrishna for being my well-wisher and mentor, awakening my interest in the study of Photocatalysis I express my heartfelt thanks to his patient guidance and relentless support for me to become a “better me”, personally and professionally throughout the whole period of my candidature Every session with him was like a tonic for me, always thrusting me to reach a little bit more If it were not for him, I wouldn’t have been able to cross those dead-ends, the so called chasms of my research I also earnestly wish to thank my mentor, Dr Veluru Jagadeesh Babu for his invaluable and continuous support through my entire project I have benefited greatly from his technical expertise in the research industry which enabled me to conduct the research smoothly I would like to thank Dr Venugopal for being my moral mentor and lending his unconditional support whenever I needed some I also would like to thank Dr Murugan for extending his immense support for conducting my experiments I would like to extend my gratitude to Dr Sreekumaran for giving me some valuable tips about research I am very indebted to Raji, for being my big sister and for her tireless friendship with me I thank her for traveling with me during all the ups and downs with me, throughout my roller-coaster life ride in Singapore ii Of course, this wouldn’t have been more awesome without Lingling, and Jia Lin for all those countless, interesting Chinese lessons and storytelling sessions, which made my life more bearable and beautiful I thank Naveen for all those timeless, meaning-intense talks which I will cherish forever Also, my very best friends here Gowthami, Lalitha and Venki helped me to share my load with them, which made my carrying lesser, so a huge thanks to them as well As seniors and my supporters, Padmalosini and Akila have offered me a tremendous support For that, I thank them both from the core of my heart I convey my special thanks to Anand and Hemant for those very many memorable moments, be it in or outside classes Also, though it has been a short time that I have known Laura, the moments I spent with her were probably one of my eventful times And, for applying flavours to my life and for helping me out then and there, I thank Preethi, Vasugi, Lily, Natasha, Kavitha, Aleksander Gora, Shayanti, Dr Mya, Kalaivani, Satin, Murthy, Bala, Zhao Xuan, Guo Rui, Zhao Jing, Maedeh, Elham, Wu, Dr Sridhar, Dr Sundar, Poonguzhali and Deepesh Thanks to Aravind and Karthik for all those study materials and suggestions that helped me to score good marks in my coursework I would like to extend my gratitude to the lab mates from CNN for their helping hands and support Of course, this would mean a special mention and thanks to our laboratory technologist, Ms Charlene Indeed I can’t miss to thank the Department of Mechanical Engineering for it has given me an opportunity to follow my dream and I extend the same gratitude to the Department of ETM for offering me the financial support through the Teaching Assistantship I offer very special thanks iii to our loveable, Ms Sharen for her constant support through all my administrative stuff and for her radiant & refreshing smile that she puts on while serving the students A very big thanks to Prof Marcelo Ang and Prof Charles Lee for graciously accepting me as a Teaching Assistant for their module, and Ms Mavis for helping me throughout the processes in MOT And I have to offer sincerest love and thanks to Chu Laoshi who has made a whole lot of difference in my life and motivated me greatly Thanks too to my other friends whom I might not have mentioned here but have enriched my life personally or professionally and made my stay in Singapore a lot memorable This wouldn’t be complete if I leave Shengjie, and Dr Duong for they have taught me a long way that I couldn’t have learnt elsewhere On a personal note, I thank my best buddies Arjun, Divya, Saba, Sai, Ashwin, DJ, Santra, Lavs, Kiru for always being there when I needed them And, as always I am forever indebted to My Family for having always supported me throughout my ups and downs of my life I thank My Parents for their unconditional love and dedication, my Uma Manni, Vasantha Paati and Murali maama for their caring, motivation and encouragement As a final note, I owe this all to my fairy Godmother Amma – Suganya, my beloved sister Darshini, my little brother Praveen, my everloving Appa – Rajaraman, my biological parents Ramamurthy Thatha, and Saroja Paati On a final note, my studies would never have been possible without the Almighty, Upaguru and Aadhiguru for whom I just can’t thank enough iv “If I were a bird, I would be flying definitely because of my two wings” Thanks to my two wings that helped me overcome any kind of obstacles and the only cause of my survival at Singapore I dedicate my entire Master Studies to my beloved foster parents, Vasantha Paati and Uma Manni who have both suffered a lot for me and my studies here I am forever indebted to them v Abstract Low Dimensional Bismuth (LDB) based nanomaterials have created wide interest among the research community due to the unique electronic configuration of Bi , which is helpful in boosting the mobility of photogenerated carriers and hence extensively used for photocatalytic applications Specifically, Bismuth Oxyhalides have demonstrated a huge range of applications as a pigment in the cosmetic industries, as a potential material for optoelectronic and photovoltaic devices (such as LEDs, lasers, solar panels, excellent photo-degradation material, etc.) It has also been found that BiOX (X = Cl, Br, I) in general have exhibited excellent photocatalytic activity on the degradation of Rhodamine B, and azo dyes such as Methyl Orange and Congo red under both UV and visible light irradiation Hence, it is important to investigate the growth mechanism and morphology of the low dimensional Bismuth based nanomaterials to achieve optimum photo-catalytic activity and explore the possible applications The efficient way to explore and improve the efficiency is through the morphological manipulation of nanostructured materials since we can achieve high surface to volume ratios So far, nano-materials in specific, Bismuth based nano-materials with distinct morphologies (nanotubes, nanowires, nano-flakes, nano-spheres) have, in most of the cases boosted the efficiency of the solar devices at an affordable cost range In this thesis, the morphologies of the Bi-based materials were modvi ified by changing molar concentrations of the precursors with the primary aim to improve the photocatalytic degradation of the low dimensional nano-materials under UV-light irradiation By changing the elemental composition, the photodegradation activities of Bismuth Oxide (Bi2 O3 ), Bismuth Oxy Chloride (BiOCl), Bismuth Oxy Bromide (BiOBr), and Bismuth Oxy Iodide (BiOI) were studied systematically The results showed that the Bismuth Oxyhalides fabricated by a simple electrospinning method exhibited superior photocatalytic activity under UV-light irradiation towards Alizarin Red S, a hazardous, synthetic organic dye vii Contents List of Figures xv List of Tables xvi Nomenclature xviii Introduction 1.1 1.2 1.3 Background 1.1.1 Environmental Pollution 1.1.2 Sources of Water Pollution Water Treatment 1.2.1 Treatment Methods for Pollution 1.2.2 Advanced Oxidation Processes Photocatalysis 1.3.1 Photocatalysis - Advantages 1.3.2 Classification of Photocatalysis 10 1.3.2.1 Homogeneous photo-induced oxidation 11 1.3.2.2 Heterogeneous photocatalysis 12 1.3.3 Applications of Photocatalysis 13 1.3.4 Conventional photocatalysts and their limitations 14 1.3.5 Bismuth Oxides and Bismuth Oxyhalides 15 viii 1.4 Project Objectives 16 1.5 Thesis Overview 17 Literature Review 18 2.1 Introduction 18 2.2 Photo-Oxidation Process 19 2.2.1 Basic Principles of Photocatalysis 19 2.2.2 Mechanism of Photocatalysis 20 2.2.3 Classification of Photocatalytic Systems 27 2.2.3.1 Semiconductors with dye-sensitizers 28 2.2.3.2 Semiconductor hetero-structures 29 2.2.3.3 Semiconductors doped with metal cations 29 2.2.3.4 Semiconductors doped with anions 30 Factors Influencing Photocatalytic Processes 31 2.2.4.1 Temperature 32 2.2.4.2 O2 concentration 32 2.2.4.3 Catalyst Concentration 33 2.2.4.4 Pollutant Concentration 33 2.2.4.5 Light source 34 2.2.4.6 Structure and Morphology of Photocatalyst 34 Bismuth Oxy-Compounds 35 2.3.1 Crystal structure and Properties 36 2.3.1.1 Bismuth Oxide 36 2.3.1.2 Bismuth Oxy-Halides 39 Synthesis of Bi-based photocatalysts 40 2.3.2.1 Physical route synthesis 40 2.3.2.2 Chemical route synthesis 42 Dye Selection 51 2.2.4 2.3 2.3.2 2.4 ix ... Photocatalytic Performance of Nanofibrous Bismuth Oxy- Nanomaterials 81 5.1 Introduction 81 5.2 Photocatalytic activity of Bi2 O3 82 5.3 Photocatalytic. .. Evaluation of photocatalytic activity 61 3.3.2 3.4 Electron Microscopy Synthesis and Characterization of Electrospun Nanofibrous Bismuth Oxide based Photocatalytic. .. extensively used for photocatalytic applications Specifically, Bismuth Oxyhalides have demonstrated a huge range of applications as a pigment in the cosmetic industries, as a potential material for optoelectronic