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 luan an 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. NGUYEN VAN HIEU Hanoi – 2020 luan an 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. 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 PhD. Nguyen Van Hieu Nguyen Van Hoang luan an 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. Nguyen Duc Hoa, Assoc. 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 103.25 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. Student Nguyen Van Hoang luan an CONTENTS CONTENTS. i ABBREVIATIONS AND SYMBOLS. v LIST OF TABLES.
vii LIST OF FIGURES. OVERVIEW ON SMO NFs AND THEIR LOADING WITH RGO FOR GAS-SENSING APPLICATION. Electrospinning for NFs fabrication. Background on electrospinning.
Processing – structure relationships of electrospun NFs. NFs for gas-sensing application. Electrospun SMO NFs for gas-sensing application. Electrospun SMO NFs for H2S gas-sensing application.
Electrospun SMO NFs for H2S gas-sensing application. NFs loading with RGO for gas-sensing application. Overview on RGO and its application in gas-sensing field. Overview on RGO.
RGO in gas-sensing application. RGO-loaded SMO NFs in gas-sensing applications. RGO-loaded SMO gas sensor. RGO-loaded SMO NFs gas sensor.
Gas-sensing mechanism. Gas-sensing mechanism of SMO NFs. Gas-sensing mechanism of RGO-loaded SMO NFs. H2S gas-sensing mechanism of SMO NFs and their loading with RGO….
27 Conclusion of chapter 1. α-Fe2O3 NFs preparation. ZFO NFs preparation. Preparation of α-Fe2O3, ZFO NFs loading with RGO.
SEM and EDX. TEM and SAED. Gas-sensing measurement. 35 Conclusion of chapter 2.
α-Fe2O3 NFs AND THEIR LOADING WITH RGO FOR H2S GAS- SENSING APPLICATION. H2S gas sensors based on α-Fe2O3 NFs. Morphologies and structures of α-Fe2O3 NFs. 39 ii luan an 3.
H2S gas-sensing properties of α-Fe2O3 NFs sensors. Effects of operating temperature. Effects of solution contents. Effects of annealing temperature and electrospinning time.
Selectivity and stability. H2S gas sensors based on α-Fe2O3 NFs loaded with RGO. Morphologies and structures of α-Fe2O3 NFs loaded with RGO. H2S gas-sensing properties of RGO-loaded α-Fe2O3 NFs sensors.
Effects of RGO contents. Effects of working temperature. Effects of annealing temperatures. Selectivity and stability.
64 Conclusion of chapter 3. ZFO NFs AND THEIR LOADING WITH RGO FOR H2S GAS- SENSING APPLICATION. H2S gas sensors based on ZFO NFs. Gas-sensing properties.
Effects of the operating temperature. Effects of the annealing temperature. Effects of annealing time and heating rate. Selectivity and stability.
H2S gas sensors based on ZFO NFs loaded with RGO. 82 iii luan an 4. Gas-sensing properties. Effects of RGO contents.
Effects of operating temperature. Effects of annealing temperatures. Selectivity, stability and RH effects. 91 Conclusion of chapter 4.
94 CONCLUSIONS AND RECOMMENDATIONS. 95 LIST OF PUBLICATIONS. 117 iv luan an ABBREVIATIONS AND SYMBOLS Number Abbreviations and Meaning symbols 1 1D One Dimension 2 2D Two Dimension 3 CVD Chemical Vapor Deposition 4 DI Deionized Water 5 DL Detection Limit 6 DMF Dimethylformamide 7 DTG Derivative Thermogravimetric 8 EDX Energy Dispersive X-ray spectroscopy Field Emission Scanning Electron 9 FE-SEM Microscope 10 FFT Fast Fourier Transform 11 GO Graphene Oxides 12 GP Graphene High Resolution Transmission Electron 13 HRTEM Microscope International Union of Pure and Applied 14 IUPAC Chemistry Joint Committee on Powder Diffraction 15 JCPDS Standards 16 NFs 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 Million 24 PVA Poly(vinyl alcohol) 25 RGO Reduced Graphene Oxides 26 RH Ambient Relative Humidity 27 RT Room Temperature v luan an 28 SAED Selected Area Electron Diffraction 29 sccm Standard Cubic Centimeters Per Minute 30 SEM Scanning Electron Microscope 31 SMO Semiconductor Metal Oxides 32 TEM Transmission Electron Microscope 33 TGA Thermogravimetric Analysis 34 WF Work Function 35 XRD X-ray Diffraction 36 ZFO Zinc Ferrite, ZnFe2O4 37 Ra Sensor resistance in dry air 38 Rg Sensor resistance in tested gas 39 S Sensor Response 40 τres Response time 41 τrec Recovery time vi luan an LIST OF TABLES Table 1. SMO NFs for gas-sensing application.
Processing parameter of of α-Fe2O3 NFs, ZFO NFs and their loading with RGO. Different nanostructures of α-Fe2O3 for H2S gas-sensing application. α-Fe2O3 loaded with RGO for gas-sensing application. Different nanostructures of ZFO for H2S gas-sensing application.
Comparison of the H2S gas sensitivity of the sensor based on other nanomaterials and nanostructures. Calculation table of DL to H2S of sensors based on α-Fe2O3 NFs loaded with different contents of RGO from 0 to 1.5 wt% RGO at 350°C. Calculation table of DL to H2S of α-Fe2O3 NFs sensors calcined at annealing temperatures from 400°C to 800°C at 350°C. Calculation table of DL to H2S of 1.% RGO-loaded α-Fe2O3 NFs sensors calcined at annealing temperatures from 400°C to 800°C at 350°C.
Average nanograin sizes determined by Scherrer formula and integrated intensity of (311) diffraction peak of ZFO-NFs calcined at different conditions. Response and response-recovery time to 1 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 (0.5−20°C/min), electrospinning time (10−120 min). Calculation table of DL to H2S of the ZFO NFs sensors calcined at the annealing temperature from 400°C to 700°C at 350°C. Calculation table of DL to H2S of the 1 wt% RGO-loaded ZFO NFs sensors calcined at annealing temperatures from 400°C to 700°C at 350°C.
123 vii luan an LIST OF FIGURES Figure 1.1: Schematic diagram of electrospinning method: 1-Collector, 2-As-spun fibers, 3-Precursor solution, 4- Syringe, 5-Needle, 6- DC voltage power supply. Kind of collectors and needles: (a) plate collector (b) Multiple spinnerets (c) Coaxial spinneret (d) Bicomponent spinneret (e) Disc collector , (d) Rotating drum [33]. FESEM images of ZnO NFs (a) as-spun, (b) calcined at 600°C in air. Number of annual publications on “graphene” and “graphene and sensors” according to Scopus Database.
The dashed lines are exponential fitting of the number of publications. Inset is where “graphene and sensors” publications have appeared [64]. Scotch –tape method [65]. Histogram detailing the number of graphene-based gas/vapor sensors publications per year for the period from 2007 to 2014 (data obtained from ISI Web of Knowledge, January 28, 2015) ) [72].
(a) Schematic of the novel gas-sensing platform of an RGO sheet decorated with SnO2 nanocrystal. SEM and TEM images of (a,b) RGO-loaded ZnO NFs and (c-d) RGO- loaded SnO2; Sensor response of (e) RGO-loaded ZnO NFs and (f) RGO-loaded SnO2; (g) Comparision of of pure SnO2 NFs, pure ZnO NFs, rGO-loaded SnO2 NFs and rGO-loaded ZnO NFs to 10 ppm H2 gas [91]. Schematic illustration of sensing mechanism of pure n-ZnO NFs [11,180]. Schematic illustration of sensing mechanism of RGO-loaded ZnO NFs [11].
26 viii luan an Figure 1. Schematic illustration of sensing mechanisms with respect to NO2 gas RGO-loaded SnO2 NFs [94]. (a) Schematic of on-chip fabrication of NF sensors by electrospinning: (1) collector, (2) Pt electrodes, (3) DC high voltage power supply, (4) as-spun nanofibers, (5) needle, (6) syringe; (b-d) FESEM images of on-chip NFs. Schematic diagram of the gas-sensing system [113].
Crystal structure of α-Fe2O3 [119]. TGA curve for decomposition of as-spun α-Fe2O3 fibers. XRD patterns of as-spun fibers and α-Fe2O3 NFs calcined calcined at different annealing temperatures (400 − 800°C) for 3 h in air. FESEM images of as-spun and α-Fe2O3 NFs prepared with various PVA concentrations: 7 (a, d), 11 (b, e), and 15 wt% (c, f), respectively.
Insets are low- magnification images. FESEM images of as-spun and α-Fe2O3 NFs prepared with different ferric salt concentrations: 2 wt% (a, d), 4 wt% (b, e), and 8 wt% (c, f), respectively. Insets are low-magnification images. FESEM images of the α-Fe2O3 NFs sensors prepared at electrospun time of 10 (a), 30 (b), 60 (c), and 120 min (d).
FESEM images of as-spun fibers (a) and α-Fe2O3 NFs prepared at different annealing temperatures: 400°C (b), 500°C (c), 600°C (d), 700°C (e), and 800°C (f). Inset figures are low-magnification images. TEM images at different magnifications (a-b), HRTEM image (c) with corresponding fast Fourier transform (FFT) inset image, and EDX spectrum (d) of α-Fe2O3 NFs calcined at 600°C for 3 h in air. Sensing transients of α-Fe2O3 NF sensors to 1 ppm H2S at various operating temperatures (a), sensor resistances (b), sensor response (c), response time and recovery time (d) as a function of operating temperatures.
Schematic of the gas-sensing mechanism of the α-Fe2O3 NFs: in air (a) and in H2S gas (b). 48 ix luan an Figure 3. H2S sensing transients of α-Fe2O3 NF sensors with various PVA concentrations (a−c) and different ferric salt concentrations (d−f). Sensor response to H2S gas as a function of PVA concentrations (g) and ferric salt concentrations (h).
H2S sensing transients of α-Fe2O3 NF sensors with various annealing temperatures (400−800°C) (a−e) and different electrospinning time (10−120 min) (e−h). Sensor response to H2S gas as a function of annealing temperatures (i) and electrospinning time (k). Selectivity to various gases at 350°C (a) and stability at 1 ppm H2S gas at 350°C (b) of the sensors based on α-Fe2O3 NFs calcined at 600°C. XRD patterns (a), Raman spectrum (b) SEM image (c) and TGA curves (d) of synthesized RGO.
FESEM images of the α-Fe2O3 NFs loaded by RGO of various concentrations: 0 (a), 0. FESEM images of 1.0 wt% RGO loaded α-Fe2O3: as-spun (a) and calcined at 400 (b), 500 (c), 600 (d), 700 (e), and 800°C (f) for 3 h in air. XRD patterns (a) and EDX spectrum (b) of α-Fe2O3 NFs annealed at 600°C for 3 h in air. TEM images at different magnifications (a-b), SAED pattern (c), and HRTEM image (d) with corresponding fast Fourier transform (FFT) inset image of 1%wt RGO loaded α-Fe2O3 annealed at 600°C for 3 hours in air.
H2S sensing transients of α-Fe2O3 NFs sensors loaded with different RGO concentrations: 0 (a), 0.