Synthesis an voc gas sensing characteristics of nanostructured cofe2o4

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY MASTER THESIS Synthesis and VOC gas sensing characteristics of nanostructured CoFe2O4 NGUYEN DUC HOANG LONG Long.NDH202554M@sis.hust.edu.vn Specialized: Electronic materials Supervisor: Professor PhD Nguyen Duc Hoa Signature of Supervisor Institute: International Training Institute for Materials Science (ITIMS) HANOI, 05/2022 SOCIALIST REPUBLIC OF VIETNAM Independence - Freedom - Happiness CONFIRMATION OF MASTER’S THESIS ADJUSTMENT Full name of author: Nguyen Duc Hoang Long Synthesis and VOC gas sensing characteristics of nanostructured CoFe2O4 Major: Materials Science Student ID: 20202554M The author, the supervisor, and the Committee confirmed that the author has adjusted and implemented the thesis according to the report of the Committee on May 19th, 2022 with the following contents: The thesis has been corrected for typographical errors and printing according to the opinions of the committee’s members June 2nd, 2022 Supervisor Author Prof Nguyen Duc Hoa Nguyen Duc Hoang Long COMMITTEE’S CHAIRMAN Prof Vu Ngoc Hung DECLARATION I declare that the content of this thesis is my research work under the guidance of Prof PhD Nguyen Duc Hoa The data and results in this thesis are completely honest and have not been published by other authors Hanoi, 6th May, 2022 Supervisor Student Professor PhD Nguyen Duc Hoa Nguyen Duc Hoang Long i ACKNOWLEDGEMENT First of all, I would like to express my deep gratitude to Prof PhD Nguyen Duc Hoa He has contributed valuable scientific ideas as well as create favorable conditions for me to scientific research and complete this thesis In addition to this, I would like to express my sincere thanks to the teachers, and staff at the Laboratory of Research, Development, and Application of Nanosensors - International Training Institute for Materials Science (ITIMS) for enthusiastically guided as well as supported me a lot during my study and scientific research Studying and researching in a new environment is very surprising, but thanks to the dedicated guidance of the teachers and brothers and sisters, I have learned lots of salutary knowledge Furthermore, I am very grateful to Dr Nguyen Hong Hanh and PhD student Lai Van Duy for supporting and sharing work experiences Moreover, I would like to thank the International Training Institute for Materials Science, the Institute of Engineering Physics, and the Training Department - Hanoi University of Science and Technology for creating conditions for me to study and research Finally, I would like to thank my family, colleagues, and friends for their support and encouragement during difficult times so that I could overcome and complete this thesis Hanoi, 6th May, 2022 STUDENT NGUYEN DUC HOANG LONG ii CONTENTS DECLARATION i ABBREVIATIONS v LIST OF TABLES vi LIST OF FIGURES vii INTRODUCTION 1 Foundation of the thesis Aims of the thesis 3 Research object and research scope 4 Research method The practical meaning of the thesis The novel statements of the thesis The strcture of the thesis CHAPTER OVERVIEW 1.1 Volatile organic compounds (VOCs) 1.2 Overview of CoFe2O4 nanomaterials 1.3 1.2.1 Crystal structure of CoFe2O4 nanomaterials 1.2.2 CoFe2O4 material in gas sensor application 12 1.2.3 Gas-sensing mechanism of metal oxide semiconducting 16 Synthesis and modification methods of CoFe2O4 nanomaterials 20 1.3.1 Hydrothermal method 20 1.3.2 Modification method of CoFe2O4 material 22 CHAPTER EXPERIMENTAL 24 2.1 The synthesis process of CoFe2O4 nanostructure by hydrothermal method 24 2.1.1 2.2 Equipment and chemicals 24 Synthesis of CoFe2O4 nanostructured materials with different structural morphology by hydrothermal method 24 2.3 The process of modifying Ag/Pt nanoparticles on the surface of CoFe2O4 nanomaterials 26 2.3.1 Process of systhesis Pt nanoparticles by polyol method 26 2.3.2 The manufacturing process of Ag/Pt nanoparticles 27 iii 2.3.3 The process of modifying Ag/Pt nanoparticles on the surface of CoFe2O4 nanorods 28 2.3.4 Sensor manufacturing process 29 2.4 Methods of investigation and analysis of materials 29 2.5 Survey of gas-sensing properties 30 CHAPTER RESULTS AND DISCUSSION 32 3.1 Morphology and crystal structure of CoFe2O4 materials synthesized by hydrothermal method 32 3.1.1 Effect of hydrothermal temperature on morphology and structure of CoFe2O4 materials 32 3.1.2 Effect of hydrothermal time on structure and morphology of CoFe 2O4 materials 37 3.2 Gas-sensitive properties of CoFe2O4 materials with different structure and morphology 42 3.3 Research on surface modification of CoFe2O4 nanorods by Ag/Pt nanoparticles to improve gas-sensing characteristics 50 3.3.1 Morphology and structure of Ag/Pt nanoparticles 50 3.3.2 Morphology and microstructure of CoFe2O4 nanomaterials before and after surface decoration with Ag/Pt nanoparticles 51 3.3.3 Gas-sensing properties of Ag/Pt decorated CoFe2O4 nanorods 55 CONCLUSIONS AND RECOMMENDATIONS 65 LIST OF REFERANCES 67 iv ABBREVIATIONS Number Abbreviations and symbols Meaning SEM Scanning Electron Microscope TEM Transition Electron Microscope UV-Vis Ultraviolet - visible BET Brunauer- Emnet-Teller EDS/EDX Energy-dispersive X-ray spectroscopy XRD X-ray Diffraction ppb Parts per billion ppm Parts per million Ra Rair 10 Rg Rgas 11 S Sensitivity 12 CVD Chemical Vapour Deposition 13 JCPDS 15 ads Adsorption 16 PVA Polyvinyl alcohol – (C2H4O)x 17 VOCs Volatile Organic Compounds Joint Committee on Powder Diffraction Standards v that of pure CFO sensor As the rate of spillover increases, more reaction sites are created on the surface of the material, which means that it allows the gas molecules to more easily react with the previously adsorbed oxygen ions and release electrons, thereby increasing the reaction with acetone gas As a result, when exposed to acetone, the released electrons recombine with holes and lead to a decrease in the hole concentration, the resistance of Ag/Pt-CFO sensor is thus increased After refreshing the sensing chamber with dry air, the oxygen molecules in air were again adsorbed onto the surface of the Ag/Pt-CFO nanorods, and then the sensor resistance returned to its initial values 64 CONCLUSIONS AND RECOMMENDATIONS After the implementation of the topic and based on the analysis results presented above, we draw some conclusions as follows: - Successfully fabricated several CoFe2O4 nanostructures with different morphology by a simple hydrothermal method - Sensors with gas-sensitive membranes of CoFe2O4 nanomaterials with different morphology have been fabricated by coating technique The sensors have good durability, material adhesion and stability during the investigation of gas sensitivity to VOCs (acetone, methanol, ethanol, toluene, and isopropanol) The results show that the CFO_120_24 sensor has relatively good sensitivity, selectivity and stability to acetone gas at a working temperature of 350 °C The CFO_120_24 sensor showed the response value to 500 ppm acetone at 350 oC of 1.67 - Successfully studied and fabricated Ag/Pt nanoparticles by reducing method (Poloy) in Ethylene Glycol (EG) solvent The thesis has studied and successfully modified Ag/Pt nanoparticles on the surface of CoFe2O4 nanorods by drop-casting method to improve the acetone gas sensitivity of the material Controlling the density of Ag/Pt nanoparticles by varying the mass ratio of Ag/Pt nanoparticles to the mass of CoFe2O4 - Gas sensor based on the modification of Ag/Pt nanoparticles on CoFe2O4 material with a content of wt.% (Ag/Pt1-CFO) has improved response and reduced response/recovery time for acetone compared with the unmodified CoFe2O4 sensor The Ag/Pt1-CFO sensor measured at 350 °C showed the response value of 3.21 to 500 ppm acetone (enhance of 92%) However, besides the results that the thesis has achieved, there are still many issues that need to be studied further Therefore, the next research direction is: • Continue to study the influence of other hydrothermal conditions on the formation of different structural morphology of CoFe2O4, to enhance the sensitivity to VOCs 65 • In addition, we plan to investigate the denaturation with other metals such as Ag/Pd, Pd, Ag, or in combination with other metal oxide materials to improve gas sensitivity, selectivity, and the working temperature of the sensor 66 LIST OF REFERANCES A Nayyar and V Puri, ―Data Glove: Internet of Things (IoT) Based Smart Wearable Gadget,‖ Br J Math Comput Sci., vol 15, no 5, pp 1–12, Jan 2016, doi: 10.9734/BJMCS/2016/24854 [2] Q Xu, P Ren, H Song, and Q Du, ―Security Enhancement for IoT Communications Exposed to Eavesdroppers With Uncertain Locations,‖ IEEE Access, vol 4, pp 2840–2853, 2016, doi: 10.1109/ACCESS.2016.2575863 [3] L M Dang, M J Piran, D Han, K Min, and H Moon, ―A Survey on Internet of Things and Cloud Computing for Healthcare,‖ Electronics, vol 8, no 7, p 768, Jul 2019, doi: 10.3390/electronics8070768 [4] J Lelieveld, J S Evans, M Fnais, D Giannadaki, and A Pozzer, ―The 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Aims of the thesis... structure of inverse spinel lattice of CoFe2O4 [65] 11 Figure 1.4 The total density of state and band structure of CoFe2O4 [69] 12 Figure 1.5 FESEM and TEM images of the precursors of (A, B) CoFe2O4. .. Overview of CoFe2O4 nanomaterials 1.3 1.2.1 Crystal structure of CoFe2O4 nanomaterials 1.2.2 CoFe2O4 material in gas sensor application 12 1.2.3 Gas- sensing mechanism of metal