Electrospun Polyaniline-Reduced Graphene Oxide Composite Nanofibers Based High Sensitive Ammonia Gas Sensor Supervisors: Prof.ª Dr.ª Cristina Delerue Matos Dr. Viswanathan Subramanian This page has been deliberately left blank. 2 Acknowledgements I was honored to have the opportunity to work with Dr. S. Viswanathan and would like to acknowledge his guidance, direction, advice, support and humor through this entire project. Special thanks also go to Dra. Cristina Delerue Matos for hosting me in its lab, for its support, humor and focus along the work. My thanks also go to my colleagues and friends in the GRAQ group, who came to my rescue when I needed and helped me to keep me grounded and sane. My parents have always been my staunchest supporters. Finally, I would like to thank my girlfriend, for always being there. 3 This page has been deliberately left blank. 4 Index Abstract ............................................................................................................................. 15 Resumo .............................................................................................................................. 17 Chapter 1 Introduction ............................................................................................................ 19 Introduction .................................................................................................................... 21 Chapter 2 Ammonia ................................................................................................................. 23 2.1. Introduction ............................................................................................................. 25 2.2. Physical Properties................................................................................................... 25 2.3. Chemical Properties ................................................................................................. 27 2.4. Dangers in handling ammonia ................................................................................. 28 2.4.1. Classification according to Regulation (EC) No 1272/2008 [CLP/GHS] .......... 28 2.5. Ammonia production ............................................................................................... 29 2.6. Sources of ammonia ................................................................................................ 30 Chapter 3 Areas of application ................................................................................................ 33 3.1. Introduction ............................................................................................................. 35 3.2. Analysis of the environmental gas ........................................................................... 35 3.3. Automobile industries .............................................................................................. 36 3.3.1. Exhaust gases .................................................................................................... 36 3.3.2. Air quality control in vehicles cockpit .............................................................. 36 3.3.3. NOX reduction in diesel engines ....................................................................... 36 3.4. Chemical industries ................................................................................................. 37 3.5. Medical industries .................................................................................................... 37 3.5.1. Human health hazards ....................................................................................... 37 3.5.2. Medical interest in ammonia sensing ................................................................ 38 3.6. Final considerations ................................................................................................. 43 Chapter 4 Ammonia gas measurement principles ................................................................. 45 4.1. Introduction ............................................................................................................. 47 5 4.2. Metal oxide ammonia gas sensors ........................................................................... 47 4.3. Surface acoustic wave ammonia gas sensors ........................................................... 49 4.4. Catalytic ammonia gas sensors ................................................................................ 49 4.5. Optical ammonia gas analyzers................................................................................ 50 4.5.1. Spectrophotometric ammonia gas detection ...................................................... 50 4.5.2. Ammonia determination by optical absorption ................................................. 51 4.6. Indirect ammonia gas measurement with nonselective detectors ............................. 52 4.7. Conducting polymers for ammonia gas detection .................................................... 53 4.7.1. Introduction ...................................................................................................... 53 4.7.2. Polyaniline as organic material ......................................................................... 53 4.7.3. Polyaniline as sensing layer .............................................................................. 54 4.7.4. Ways of synthesizing polyaniline ..................................................................... 55 4.7.5. Polyaniline doping ............................................................................................ 56 4.7.6. Deposition methods of PANI layers.................................................................. 57 4.7.7. Polyaniline and inorganic substrates ................................................................. 59 4.8. Metal oxide with conducting polymers sensors ....................................................... 60 4.9. Final considerations ................................................................................................. 62 Chapter 5 Transduction modes on PANI layers ..................................................................... 63 5.1. Introduction ............................................................................................................. 65 5.2. Electrical conductivity variations ............................................................................. 65 5.2.1. Dopant nature ................................................................................................... 65 5.2.2. Substituents on aniline ring ............................................................................... 67 5.2.3. Sensing layer deposition method ...................................................................... 68 5.3. Electrical conductivity characteristics on field effect transistor ............................... 68 5.4. Electrical conductivity characteristics of optical parameter ..................................... 69 Chapter 6 PANI nanostructures .............................................................................................. 71 6.1. Introduction ............................................................................................................. 73 6.2. Elaboration of polyaniline nanofibers ...................................................................... 73 6 6.2.1. Physical techniques ........................................................................................... 73 6.2.2. Polymerization of aniline by chemical oxidation .............................................. 74 6.2.3. Polymerization of aniline by electrochemical oxidation ................................... 75 6.3. Polyaniline nanofibers properties and structure ....................................................... 75 Chapter 7 Electrospinning technique in the formation of PANI nanofibers ........................ 77 7.1. Introduction ............................................................................................................. 79 7.2. Electrospinning principle ......................................................................................... 79 7.3. Electrospinning process parameters ......................................................................... 80 7.3.1. Solution properties ............................................................................................ 81 7.3.2. Process conditions............................................................................................. 81 7.3.3. Ambient conditions ........................................................................................... 82 7.4. Polyaniline nanostructures by electrospinning ......................................................... 82 7.4.1. Polyaniline nanofibers ...................................................................................... 82 Chapter 8 Graphene ................................................................................................................. 85 8.1. Introduction ............................................................................................................. 87 8.2. Graphene oxide (GO) .............................................................................................. 87 8.3. Reduced graphene oxide (RGO) .............................................................................. 88 8.4. Polymer-graphene composites ................................................................................. 89 Chapter 9 Experiments ...........................................................................................................