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MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY Nguyen Van Hoang ELECTROSPINNING OF α-Fe2O3 AND ZnFe2O4 NANOFIBERS LOADED WITH REDUCED GRAPHENE OXIDE (RGO) FOR H2S GAS SENSING APPLICATION DOCTORAL DISSERTATION OF MATERIALS SCIENCE Hanoi – 2020 MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY Nguyen Van Hoang ELECTROSPINNING OF α-Fe2O3 AND ZnFe2O4 NANOFIBERS LOADED WITH REDUCED GRAPHENE OXIDE (RGO) FOR H2S GAS SENSING APPLICATION Major: Materials Science Code: 9440122 DOCTORAL DISSERTATION OF MATERIALS SCIENCE SUPERVISOR: PROF PhD NGUYEN VAN HIEU Hanoi – 2020 DECLARATION OF AUTHORSHIP This dissertation has been written in the basic of my researches carried out at Hanoi University of Science and Technology, under the supervision of Prof PhD Nguyen Van Hieu All the data and results in the thesis are true and were agreed to use in my thesis by co-authors The presented results have never been published by others Hanoi, 16th January 2020 Supervisor Prof PhD Nguyen Van Hieu PhD Student Nguyen Van Hoang ACKNOWLEDGMENTS First, I would like to express my deep gratitude to my supervisor, Prof Nguyen Van Hieu, for his devotion and inspiring supervision I would like to thank him for all his advice, support and encouragement throughout my postgraduate course I am grateful to Assoc Prof PhD Nguyen Duc Hoa, Assoc Prof PhD Nguyen Van Duy, PhD Dang Thi Thanh Le, PhD Chu Manh Hung, and PhD Nguyen Van Toan for their useful help, suggestions and comments I also would like to express my special thanks to PhD and Master Students at iSensors Group for their support and shared cozy working environment during my PhD course I am thankful to the leaders and staffs of International Training Institute for Materials Science (ITIMS), Graduate School for their help and given favorable working conditions I would like to thank my colleagues at Department of Materials Science and Engineering at Le Quy Don Technical University for their support during my PhD course I gratefully acknowledge the fund from Vietnam National Foundation for Science and Technology Development (NAFOSTED) under code 103.02-2017.25 and the 911 Scholarship of Ministry of Education and Training for the financial support for my research Last but not least, I am deeply thankful to my family for their endless love and unconditional support Without them, the work would have been impossible PhD Student Nguyen Van Hoang CONTENTS CONTENTS i ABBREVIATIONS AND SYMBOLS v LIST OF TABLES vii LIST OF FIGURES viii INTRODUCTION CHAPTER OVERVIEW ON SMO NFs AND THEIR LOADING WITH RGO FOR GAS-SENSING APPLICATION 1.1 Electrospinning for NFs fabrication 1.1.1 Background on electrospinning 1.1.2 Processing – structure relationships of electrospun NFs 1.2 NFs for gas-sensing application 10 1.2.1 Electrospun SMO NFs for gas-sensing application 10 1.2.2 Electrospun SMO NFs for H2S gas-sensing application 13 1.3 1.2.2.1 H2S gas 13 1.2.2.2 Electrospun SMO NFs for H2S gas-sensing application 13 NFs loading with RGO for gas-sensing application 14 1.3.1 Overview on RGO and its application in gas-sensing field 14 1.3.1.1 Overview on RGO 14 1.3.1.2 RGO in gas-sensing application 17 1.3.2 RGO-loaded SMO NFs in gas-sensing applications 19 1.3.2.1 RGO-loaded SMO gas sensor 19 1.3.2.2 RGO-loaded SMO NFs gas sensor 22 i 1.4 Gas-sensing mechanism 24 1.4.1 Gas-sensing mechanism of SMO NFs 24 1.4.2 Gas-sensing mechanism of RGO-loaded SMO NFs 25 1.4.3 H2S gas-sensing mechanism of SMO NFs and their loading with RGO… 27 Conclusion of chapter 28 CHAPTER EXPERIMENTAL APPROACH 29 2.1 Synthesis 29 2.1.1 RGO preparation 29 2.1.2 α-Fe2O3 NFs preparation 30 2.1.3 ZFO NFs preparation 31 2.1.4 Preparation of α-Fe2O3, ZFO NFs loading with RGO 32 2.2 Characterization Techniques 32 2.2.1 Raman spectroscopy 32 2.2.2 Thermal analysis 33 2.2.3 X-ray diffraction 33 2.2.4 SEM and EDX 34 2.2.5 TEM and SAED 34 2.3 Gas-sensing measurement 35 Conclusion of chapter 36 CHAPTER α-Fe2O3 NFs AND THEIR LOADING WITH RGO FOR H2S GASSENSING APPLICATION 37 3.1 Introduction 37 3.2 H2S gas sensors based on α-Fe2O3 NFs 39 3.2.1 Morphologies and structures of α-Fe2O3 NFs 39 ii 3.2.2 3.3 H2S gas-sensing properties of α-Fe2O3 NFs sensors 46 3.2.2.1 Effects of operating temperature 46 3.2.2.2 Effects of solution contents 48 3.2.2.3 Effects of annealing temperature and electrospinning time 50 3.2.2.4 Selectivity and stability 53 H2S gas sensors based on α-Fe2O3 NFs loaded with RGO 54 3.3.1 Morphologies and structures of α-Fe2O3 NFs loaded with RGO 54 3.3.2 H2S gas-sensing properties of RGO-loaded α-Fe2O3 NFs sensors 58 3.3.2.1 Effects of RGO contents 58 3.3.2.2 Effects of working temperature 61 3.3.2.3 Effects of annealing temperatures 62 3.3.2.4 Selectivity and stability 64 Conclusion of chapter 65 CHAPTER ZFO NFs AND THEIR LOADING WITH RGO FOR H2S GASSENSING APPLICATION 66 4.1 Introduction 66 4.2 H2S gas sensors based on ZFO NFs 68 4.2.1 Microstructure characterization 68 4.2.2 Gas-sensing properties 74 4.3 4.2.2.1 Effects of the operating temperature 74 4.2.2.2 Effects of the annealing temperature 76 4.2.2.3 Effects of annealing time and heating rate 79 4.2.2.4 Selectivity and stability 81 H2S gas sensors based on ZFO NFs loaded with RGO 82 4.3.1 Microstructure characterization 82 iii 4.3.2 Gas-sensing properties 86 4.3.2.1 Effects of RGO contents 86 4.3.2.2 Effects of operating temperature 88 4.3.2.3 Effects of annealing temperatures 89 4.3.2.4 Selectivity, stability and RH effects 91 Conclusion of chapter 94 CONCLUSIONS AND RECOMMENDATIONS 95 LIST OF PUBLICATIONS 97 REFERENCES 98 APPENDIX 117 iv ABBREVIATIONS AND SYMBOLS Number Meaning Abbreviations and symbols 1D 2D Two Dimension CVD Chemical Vapor Deposition DI Deionized Water DL Detection Limit DMF Dimethylformamide DTG Derivative Thermogravimetric EDX FE-SEM 10 FFT Energy Dispersive X-ray spectroscopy Field Emission Scanning Electron Microscope Fast Fourier Transform 11 GO Graphene Oxides 12 GP 13 HRTEM 14 IUPAC 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loaded with different contents of RGO of (a, e), 0.5 (b, f), 1.0 (c, g), and 1.5 wt.% (d, h), respectively The sensors are tested with H2S gas at operating temperature of 350°C Table A3.1 Calculation table of DL to H2S of sensors based on α-Fe2O3 NFs loaded with different contents of RGO from to 1.5 wt% RGO at operating temperature of 350°C Samples RSS rmsnoise Slope DL (ppb) 3.66E-05 0.001913113 5.53 1.04 0.5 3.03E-05 0.00174069 6.76 0.78 2.40E-05 0.001549193 8.66 0.54 1.5 1.34E-05 0.001157584 2.44 1.42 117 Fe2O3 Cal 400 oC@ H2S & 350 oC Fifth-order polynomial fit RSS = 1.31E-5 Linear Fit Slope = 4.15 (a) (f) 1.00 Cal 500 oC@ air & 350 oC Fifth-order polynomial fit RSS = 5.12E-6 1.04 Resp Base (Ra/Rg) 1.02 1.00 1.04 Cal 600 oC@ air & 350 oC Fifth-order polynomial fit RSS = 3.66E-5 1.02 Cal 700 oC@ air & 350 oC Fifth-order polynomial fit RSS = 2.34E-5 0.98 0.96 1.04 Cal 800 oC@ air & 350 oC Fifth-order polynomial fit RSS = 1.77E-5 1.02 Cal 500 oC@ H2S & 350 oC (b) (c) (d) (e) Linear Fit Slope = 2.76 (g) Cal 600 oC@ H2S & 350 oC Linear Fit Slope = 5.53 (h) Cal 700 oC@ H2S & 350 oC Linear Fit Slope = 4.48 Resp (Ra/Rg) 1.02 - Fe2O3 Cal 400 oC@ air&350 oC (i) Cal 800 oC@ H2S & 350 oC Linear Fit Slope = 0.83 (j) 1.00 0 10 0.00 Time (s) 0.25 0.50 0.75 H2S conc (ppm) 1.00 Figure A3.2 Fitted values of RSS and slope for DL calculation of α-Fe2O3 NFs sensors calcined at various annealing temperatures of 400 (a, f), 500 (b, g), 600 (c, h), 700 (d, i), and 800°C (e, j), respectively The sensors are tested with H2S gas at operating temperature of 350°C Table A3.2 Calculation table of DL to H2S of α-Fe2O3 NFs sensors calcined at annealing temperatures from 400°C to 800°C at operating temperature of 350°C Samples RSS rmsnoise Slope DL (ppb) 400 oC 1.31E-05 0.001144552 4.15 0.83 500 oC 5.12E-06 0.000715542 2.76 0.78 600 oC 3.66E-05 0.001913113 5.53 1.04 700 oC 2.34E-05 0.001529706 4.48 1.02 800 oC 1.77E-05 0.001330413 0.83 4.81 118 wt% RGO Cal 400 oC@ air&350 oC Fifth-order polynomial fit (a) RSS = 1.67E-5 1.02 Resp Base (Ra/Rg) 1.00 0.98 1.04 1.00 1.04 Cal 800 oC@ air & 350 oC Fifth-order polynomial fit RSS = 9.0E-6 1.02 10 (g) 10 Cal 600 oC@ H2S & 350 oC Linear Fit Slope = 8.66 Cal 700 oC@ air & 350 oC (d) Fifth-order polynomial fit RSS = 4.0E-5 1.02 (f) Linear Fit Slope = 3.68 Cal 600 oC@ air & 350 oC Fifth-order polynomial fit (c) RSS = 2.40E-5 1.06 10 Linear Fit Slope = 6.00 Cal 500 oC@ H2S & 350 oC Cal 500 oC@ air & 350 oC Fifth-order polynomial fit (b) RSS = 1.21E-5 1.02 wt.% RGO Cal 400 oC@H2S&350oC (h) 10 Cal 700 oC@ H2S & 350 oC (i) Linear Fit Slope = 3.15 10 Cal 800 oC@ H2S & 350 oC (e) Resp (Ra/Rg) 1.04 (j) Linear Fit Slope = 0.14 1.00 0 Time (s) 10 0.00 0.25 0.50 0.75 H2S conc (ppm) 1.00 Figure A3.3 Fitted values of RSS and slope for DL calculation of 1.0 wt.% RGO-loaded αFe2O3 NFs sensors calcined at various annealing temperatures of 400 (a, f), 500 (b, g), 600 (c, h), 700 (d, i), and 800°C (e, j), respectively The sensors are tested with H2S gas at operating temperature of 350°C Table A3.3 Calculation table of DL to H2S of 1.0 wt.% RGO-loaded α-Fe2O3 NFs sensors calcined at annealing temperatures from 400°C to 800°C at operating temperature of 350°C Samples RSS rmsnoise Slope DL (ppb) 400 oC 1.67E-05 0.001292285 0.65 500 oC 1.21E-05 0.0011 3.68 0.90 600 oC 2.40E-05 0.001549193 8.66 0.54 700 oC 4.05E-05 0.002012461 3.12 1.94 800 oC 9.00E-06 0.000948683 0.14 20.33 119 Table A4.1 Average nanograin sizes determined by Scherrer formula and integrated intensity of (311) diffraction peak of ZFO-NFs calcined at different conditions Samples β (FWHM) (radian) Crystallite sizes (nm) Integrated intensity 400 oC 0.62 13.53 20.24 500 oC 0.55 15.16 22.44 600 oC 0.46 18.08 35.39 700 oC 0.35 23.92 84.24 0.5 h 0.51 16.32 24.68 3h 0.46 18.08 35.39 12 h 0.38 21.82 69.01 48 h 0.36 23.28 108.82 0.5 oC/min 0.46 18.08 35.39 oC/min 0.68 12.25 29.19 oC/min 0.61 13.63 35.29 20 oC/min 0.55 15.23 46.58 120 Table A4.2 Response and response-recovery time to ppm H2S gas at the operating temperature of 350°C of the ZFO NFs sensors calcined at different annealing temperatures (400−700°C), annealing time (0.5−48 h), heating rates (0.5−20°C/min), electrospinning time (10−120 min) S τres τrec 1ppm (s) (s) 400 oC 8.5 47 423 500 oC 61 261 600 oC 102 206 700 oC 21.8 129 0.5 h 34 217 3h 102 206 12 h 42.3 63 48 h 15.4 40 0.5 oC/min 102 206 oC/min 19.9 53 oC/min 53.4 68 20 oC/min 7.4 12 122 Samples 121 Cal 400 oC@ H2S & 350 oC Cal 400 oC@ air & 350 oC Fifth-order polynomial fit RSS = 1.37E-5 (a) Linear Fit Slope = 8.32664 Resp Base (Ra/Ra) 1.04 Cal 500 oC@ air & 350 oC Fifth-order polynomial fit RSS = 3.69E-5 (b) 1.02 10 (e) Cal 500 oC@ H2S & 350 oC 50 Linear Fit Slope = 67.70817 (f) 1.00 25 o o o Cal 600 C@ H2S & 350 C Cal 600 C@ air & 350 C Fifth-order polynomial fit RSS = 3.28E-5 (c) 1.02 o Linear Fit Slope = 113.96252 100 (g) 1.00 50 (d) 1.02 o Cal 700 oC@ H2S & 350 oC o Cal 700 C@ air & 350 C Fifth-order polynomial fit RSS = 4.78E-6 20 Linear Fit Slope = 22.34538 (h) 1.00 10 0 10 0.00 0.25 0.50 0.75 1.00 H2S conc (ppm) Time (s) Figure A4.1 Fitted values of RSS and slope for DL calculation of the sensors based on ZFO NFs calcined at various annealing temperatures of 400 (a,e), 500 (b,f), 600 (c,g), and 700°C (d,h), respectively The sensors are tested with H2S gas at the operating temperature of 350°C Table A4.3 Calculation table of DL to H2S of the ZFO NFs sensors calcined at the annealing temperature from 400°C to 700°C at the operating temperature of 350°C Samples RSS rmsnoise Slope DL (ppb) 400 oC 1.37E-05 0.00117161 8.32664 0.422 500 oC 3.69E-05 0.00192032 67.70817 0.085 600 oC 3.28E-05 0.001810392 113.96252 0.048 700 oC 4.78E-06 0.002185514 22.34538 0.093 122 Resp (Ra/Rg) 1.06 Cal 400 oC@ air & 350 oC Fifth-order polynomial fit RSS = 5.05E-5 (a) 1.00 50 Cal 400 oC@ H2S & 350 oC Linear Fit Slope = 48.94 (e) 25 1.02 Cal 500 oC@ air & 350 oC Fifth-order polynomial fit RSS = 5.57E-5 (b) 1.00 0.98 1.04 o o Cal 600 C@ air & 350 C Fifth-order polynomial fit RSS = 3.28E-5 (c) 1.02 o 75 o Cal 500 C@ H2S & 350 C Linear Fit Slope = 86.58 50 (f) 25 Resp (Ra/Rg) Resp Base (Ra/Ra) 0.98 150 Cal 600 oC@ H2S & 350 oC Linear Fit Slope = 164.15 100 (g) 50 1.00 Cal 700 oC@ air & 350 oC Fifth-order polynomial fit RSS = 5.2E-5 (d) 1.06 Cal 700 oC@ H2S & 350 oC Linear Fit Slope = 15.25 (h) 20 10 1.04 0 10 0.00 0.25 0.50 0.75 1.00 H2S conc (ppm) Time (s) Figure A4.2 Fitted values of RSS and slope for DL calculation of the sensors based on wt% RGO loaded ZFO NFs calcined at various annealing temperatures of 400 (a,e), 500 (b,f), 600 (c,g), and 700°C (d,h), respectively The sensors are tested with H2S gas at the operating temperature of 350°C Table A4.4 Calculation table of DL to H2S of the wt% RGO-loaded ZFO NFs sensors calcined at annealing temperatures from 400°C to 700°C at the operating temperature of 350°C Samples RSS rmsnoise Slope DL (ppb) 400 oC 5.05E-05 0.002247221 48.94 0.14 500 oC 5.57E-05 0.002360085 86.58 0.08 600 oC 3.28E-05 0.001811077 164.15 0.03 700 oC 5.20E-06 0.002280351 15.25 0.44 123 ... in α -Fe2O3 and ZFO NFs for enhanced H2S gas-sensing performance Therefore, the thesis titled “Electrospinning of α -Fe2O3 and ZnFe2O4 nanofibers loaded with reduced graphene oxide (RGO) for H2S. .. Chemistry Joint Committee on Powder Diffraction Standards Nanofibers 17 NPs Nanoparticles 18 NRs Nanorods 19 NSs Nanosheets 20 NTs Nanotubes 21 NWs Nanowires 22 ppb Parts Per Billion 23 ppm Parts Per... SCIENCE AND TECHNOLOGY Nguyen Van Hoang ELECTROSPINNING OF α -Fe2O3 AND ZnFe2O4 NANOFIBERS LOADED WITH REDUCED GRAPHENE OXIDE (RGO) FOR H2S GAS SENSING APPLICATION Major: Materials Science Code: