Nhan đề : Fabrication of Zn2SnO4 nanostructures for gas sensor application = Chế tạo vật liệu Zn2SnO4 cấu trúc nano ứng dụng cho cảm biến khí Tác giả : Lai Van Duy Người hướng dẫn: Nguyen Duc Hoa Từ khoá : Vật liệu; Vật liệu Zn2SnO4 Năm xuất bản : 2020 Nhà xuất bản : Trường đại học Bách Khoa Hà Nội Tóm tắt : Tổng quan về vật liệu Zn2SnO4, cấu trúc nano; thử nghiệm; kết quả và thảo luận.
HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY MASTER THESIS Fabrication of Zn2SnO4 nanostructures for gas sensor application LAI VAN DUY Duy.LVCA180178@sis.hust.edu.vn Specialized: Electronic materials Supervisor: Professor Ph.D Nguyen Duc Hoa Institute: International Training Institute for Materials Science (ITIMS) HANOI, 6/2020 HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY MASTER THESIS Fabrication of Zn2SnO4 nanostructures for gas sensor application LAI VAN DUY Duy.LVCA180178@sis.hust.edu.vn Specialized: Electronic materials Supervisor: Professor Ph.D Nguyen Duc Hoa Institute: Signature of GVHD International Training Institute for Materials Science (ITIMS) HANOI, 6/2020 CỘNG HÒA XÃ HỘI CHỦ NGHĨA VIỆT NAM Độc lập – Tự – Hạnh phúc BẢN XÁC NHẬN CHỈNH SỬA LUẬN VĂN THẠC SĨ Họ tên tác giả luận văn: Lại Văn Duy Đề tài luận văn: Chế tạo vật liệu Zn2SnO4 cấu trúc nano ứng dụng cho cảm biến khí Chuyên ngành: Khoa học vật liệu-VLĐT Mã số SV: CA180178 Tác giả, Người hướng dẫn khoa học Hội đồng chấm luận văn xác nhận tác giả sửa chữa, bổ sung luận văn theo biên họp Hội đồng ngày 30/06/2020 với nội dung sau: - Bổ sung thích hình 3.9, 3.10, 3.13 - Các cơng thức, phương trình phản ứng đánh số theo trình tự - Bảng danh mục chữ viết tắt xếp theo thứ tự alpha b - Chữ hình 3.2, 3.4, 3.6, 3.25 để kích thước lớn - Phần thích hình có dấu chấm sau số thứ tự hình - Chỉnh sửa lỗi tả, hành văn Ngày 09 tháng 07 năm 2020 Giáo viên hướng dẫn Tác giả luận văn GS TS Nguyễn Đức Hòa Lại Văn Duy CHỦ TỊCH HỘI ĐỒNG PGS TS Nguyễn Phúc Dương ĐỀ TÀI LUẬN VĂN Chế tạo vật liệu Zn2SnO4 cấu trúc nano ứng dụng cho cảm biến khí Học viên: Lại Văn Duy Chuyên ngành: Khoa học vật liệu-VLĐT Giáo viên hướng dẫn (Ký ghi rõ họ tên) GS TS Nguyễn Đức Hòa ACKNOWLEDGEMENT First of all, I would like to express my greatest gratitude to Prof PhD Nguyen Duc Hoa for his valuable scientific ideas, guidance and support of favorable conditions for me to complete this thesis His kindness and enthusiasm will be in my heart forever Simultaneously, I would like to express my sincere thanks to all staffs of the Laboratory for Research, Development, and Application of Nanosensors at ITIMS-HUST has always been enthusiastic about helping, sharing experiences and suggesting many important ideas for me to carry out the research of this thesis Moreover, I am also very grateful to my colleagues, PhD students, the iSensors’ graduated students who have always accompanied and assisted me in two years of doing my master thesis at ITIMS Finally, I would like to thank all my family, friends and colleagues who have always encouraged and shared me to complete this thesis SUMMARY OF MASTER THESIS In this project, we developed high-performance VOC gas sensors for breath analysis by focusing on the controlled synthesis of nanostructured Zn2SnO4 ternary metal oxides to maximize the gas sensitivity To archive the objective, we synthesised hollow structure ternary metal by hydrothermal technique with the assistance of soft template The thickness of the hollow cells was optimised to desire the highest VOC response By hydrothermal method, the author has successfully synthesized many nanostructures of Zn2SnO4 with different morphologies At the same time, the thesis also proves the application potential of Zn2SnO4 material in the gas sensor VOCs The sensor based on Zn2SnO4 materials could detect various VOCs gases such as acetone, ethanol, and methanol at low concentrations of ppb levels with high sensitivity STUDENT Lai Van Duy CONTENTS ABBREVIATIONS iii LIST OF FIGURES iv LIST OF TABLES viii INTRODUCTION 1 Foundation of the thesis Aims of the thesis 3 Research object and scope of the thesis 4 Research Methods The practical and scientific significance of the thesis New contributions of the thesis The structure of the thesis CHAPTER OVERVIEW 1.1 Volatile organic compounds 1.2 Overview of Zn2SnO4 material 1.2.1 Crystal structure of Zn2SnO4 material 1.2.2 Electrical properties of Zn2SnO4 material 11 1.2.3 Application of Zn2SnO4 material in gas sensors 12 1.2.4 Gas sensitivity mechanism of metal oxide for VOCs 17 1.3 Hydrothermal method 21 CHAPTER 2.1 EXPERIMENTAL APPROACH 25 The synthesis processes of nanostructured Zn2SnO4 materials with different morphologies by hydrothermal method 25 2.1.1 Equipment and chemicals 25 2.1.2 The synthesis process of Zn2SnO4 nanostructures with different morphologies by hydrothermal method 26 2.2 Sensor manufacturing processes 29 2.3 Morphological and microstructure analysis 30 2.4 Survey of gas sensitivity properties 30 i CHAPTER 3.1 RESULTS AND DISCUSSION 32 Morphology and crystal structure of zinc Stannate nanomaterials (Zn2SnO4) synthesized by hydrothermal method 32 3.1.1 Effect of hydrothermal temperatures on the morphology of Zinc Stannate (Zn2SnO4) materials .32 3.1.2 Effect of surfactant P123 on the morphology of Zn2SnO4 material 34 3.1.3 Effect of pH on the morphology of Zn2SnO4 materials .38 3.1.4 Crystal structure of synthesized Zn2SnO4 materials 44 3.2 Gas sensing properties of Zn2SnO4 materials with different morphological structures 49 3.2.1 Methanol gas-sensing properties of the fabricated sensors 50 3.2.2 Ethanol gas-sensing properties of the fabricated sensors 53 3.2.3 Acetone gas-sensing properties of the fabricated sensors 56 CONCLUSIONS AND RECOMMENDATIONS 68 LIST OF REFERENCES 69 LIST OF PUBLICATIONS 78 ii ABBREVIATIONS Number Abbreviations and symbols Meaning ads Adsorption BET Brunauer- Emnet-Teller CVD Chemical Vapour Deposition EDS/EDX Energy-dispersive X-ray spectroscopy HRTEM High Resolution Transmission Electron Microscope IoT Internet of Things ITIMS JCPDS P123 HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H 10 ppb Parts per billion 11 ppm Parts per million 12 Ra Rair 13 Rg Rgas 14 S Sensitivity 15 SEM Scanning Electron Microscope 16 TEM Transition Electron Microscope 17 VOCs Volatile Organic Compounds 18 XRD X-ray Diffraction International Training Institute for Materials Science Joint Committee on Powder Diffraction Standards iii LIST OF FIGURES Figure 1.1 VOCs in exhaled breath can be used as biomarkers for diseases diagnose [47] Figure 1.2 Crystal structures of zinc stannate (Zn2SnO4) [51] .9 Figure 1.3 Sublattices of zinc stannate (Zn2SnO4) 10 Figure 1.4 Schematic representation of the inverse spinel lattice of Zn2SnO4 [49] 10 Figure 1.5 Model explains the n-type semiconductor of Zn2SnO4 material [50] .11 Figure 1.6 A schematic diagram of reaction mechanism of SnO2-based sensor to HCHO: (a) in air, (b) in VOCs [73] 19 Figure 1.7 Schematic energy level diagram of a metal oxide before (a) and after exposure to a VOCs (b) [43] 19 Figure 1.8 A schematic of the sensing mechanism of (a) ZnO NPs and (b) ZnO QDs in air (left) and isoprene (right) [74] 20 Figure 2.1 Photos of some of the main equipment using synthesized Zn2SnO4 nanomaterials by a hydrothermal method such as thermos flask (1), magnetic stirrer (2), pH meter (3), centrifugal rotary machine (4) and annealing furnace (5) 26 Figure 2.2 Process diagram of synthesizing Zn2SnO4 nanomaterials with different morphological structures by hydrothermal method 27 Figure 2.3 The process diagram for making sensors on the basis of nano Zn2SnO4 material by small coating method .29 Figure 2.4 (A) Gas sensitive measuring system at ITIMS; (B) Diagram of the gas measuring system by static measurement method 31 Figure 3.1 SEM image of Zn2SnO4 samples synthesized by hydrothermal method with different hydrothermal temperature: (A, B) 160 ºC; (C, D) 180 ºC; (E, F) 200 ºC 33 Figure 3.2 General diagram of synthetic Zn2SnO4 materials with different morphology according to changes in hydrothermal temperature 34 Figure 3.3 SEM image of Zn2SnO4 samples synthesized by hydrothermal method with different amount of P123 surface-active agent (A, B) g; (C, D) 0.25 g; (E, F) 0,5 g; (G, H) 1,0 g 36 iv Figure 3.4 Schematic mechanism of synthesizing Zn2SnO4 materials with different morphology by the concentration of surfactants P123 by hydrothermal method 37 Figure 3.5 SEM image of Zn2SnO4 nanomaterial synthesized by hydrothermal method with different pH conditions: (A, B) pH = 8; (C, D) pH = 9; (E, F) pH = 10; (G, H) pH = 12; (I, K) pH = 13 40 Figure 3.6 General diagram of the synthesis of Zn2SnO4 materials with different morphology according to the pH change of the hydrothermal environment 41 Figure 3.7 TEM (A-D) images of the synthesized hollow cubic Zn2SnO4 Inset of (D) is correspondent SAED 43 Figure 3.8 (A) STEM image and (B-D) EDS mapping of the hollow cubic Zn2SnO4 43 Figure 3.9 XRD samples of Zn2SnO4 with condition pH = and pH = 13 at hydrothermal temperature of 180 °C/24h 44 Figure 3.10 XRD patterns of Zn2SnO4 with condition pH = and pH =13 hydrothermal temperature of 180 °C/24h after treatment heat at 550 °C for 2h in air 45 Figure 3.11 Raman and PL spectrum of synthesized Zn2SnO4 46 Figure 3.12 BET spectra of Zn2SnO4: (A) - Octahedron, (B) - Cubic, (C) – Nanoparticles 48 Figure 3.13 I-V curve of the sensor (A) - Octahedron, (B) - Cubic, (C) – Nanoparticles measured in air at 450 oC 49 Figure 3.14 Methanol sensing characteristics of nanoparticles Zn2SnO4 (ZTO_PH8): (A) transient resistance versus time upon exposure to different concentrations of methanol measured at different temperatures; (B) sensor response as a function of methanol; (C) respon and recovery time of sensor 52 Figure 3.15 Methanol sensing characteristics of hollow cubic Zn2SnO4 (ZTOP5_PH8): (A) transient resistance versus time upon exposure to different concentrations of methanol measured at different temperatures; (B) sensor response as a function of methanol; (C) respon and recovery time of sensor 52 Figure 3.16 Methanol sensing characteristics of hollow octahedron Zn2SnO4 (ZTOP5_PH13): (A) transient resistance versus time upon exposure to different v Figure 3.26 Selectivity of sensors ZTO_PH8, ZTOP5_PH8, and ZTOP5_PH13 when surveying with different gases: acetone (100 ppm), ethanol (100 ppm), methanol (100 ppm), NH3 (25 ppm), H2 (50 ppm) and CO (5 ppm) at 450 ºC Figure 3.26 shows the sensor ZTOP5_PH13 for higher response than sensors ZTO_PH8, ZTOP5_PH8 based on hollow octahedron Zn2SnO4 for acetone gas Specifically, the sensor ZTOP5_PH13 provides a response of 44.22 times at a concentration of 125 ppm, while the response of the sensor to ethanol, reducing gases (100 ppm), methanol (100 ppm), NH3 (25 ppm), H2 (50 ppm), CO (5 ppm) only gives a response respectively of 5.90, 7.83, 5.71, 1.84 and 1.48 times For ethanol gas, the sensor ZTOP5_PH8 based on hollow cubic Zn2SnO4 material has a higher response than the two sensors ZTO_PH8 and ZTOP5_PH13 Specifically, the ZTOP5_PH8 sensor has a response of about 13.50 times at a concentration of 125 ppm, while the sensor's response to reducing gases is methanol (100 ppm), NH3 (25 ppm), H2 (50 ppm), CO (5 ppm) only gives a response, respectively of 4.64, 3.78, 1.69, 1.16 times This proves that the sensors ZTOP5_PH8, ZTOP5_PH13 on the basis of hollow cubic and hollow octahedron materials are selective for ethanol and acetone reducing gases at a working temperature of 450 ºC Therefore, from the above gas-sensitive property analysis, we believe that ZTOP5_PH8, ZTOP_PH13 sensors built on 64 the basis of a hollow cubic, hollow octahedron materials can be applied in breath analysis to detect diabetes In addition to the selectivity, the effect of ambient relative humidity (RH) on the acetone sensing properties of the sensor were also tested Figure 3.27 shows the (A, B) transient resistance and (C, D) response value versus time upon exposure to 0.5 ppm acetone measured at 450 ºC in different values of humidity of the hollow cubic, hollow octahedron Zn2SnO4 sensor The based resistance is 396, 256, 148, 66 k and 1.07 M, 1.02 M, 953 k, 859 k for 10, 60, 70, and 90% HR, respectively The decrease of based resistance with increment of relative humidity indicate that that the adsorption of water molecule donates free electrons to the conduction band of Zn2SnO4 and decrease of based resistance The response value to 0.5 ppm acetone is 2.01, 3.57, 3.16, 2.96 and 3.67, 2.89, 2.78, 2.63 in 10, 60, 70, and 90 % RH, respectively The acetone response was influenced by the ambient humidity, but at high humidity of 70-90 % RH, the variation in acetone response was ignorable Such those characteristics ensure the reliable application of gas sensor in breath analysis [21] Figure 3.27 (A, B) transient resistance and (C, D) response value versus time upon exposure to 0.5 ppm acetone measured at 450 ºC in different values of humidity of the hollow cubic, hollow octahedron Zn2SnO4 sensor 65 The gas sensing mechanism is speculated as the resistance changes of the gas sensor before and after exposure to analytic gas For n-type semiconductor metal oxide-based gas sensors, the most widely accepted gas sensing mechanism is based on the change in resistance during the adsorption and desorption of gas molecules and chemical reactions on the surface of sensing materials [91] As shown in Fig 3.28, when the sensor was exposed to ambient air, oxygen molecules adsorbed on the surface of the sensing material (Eqs (3.4)-(3.7)) captured electrons in the conduction band of Zn2SnO4 to form O2-, O-, O2- species at around 350-450 °C then generated an electron depletion layer Because the wall of the hollow cube and hollow octahedron was formed from aggregated nanocrystals, the surface of the Zn2SnO4 formed on a high potential barrier between the adjacent nanograins, leading to an increase in the resistance of the sensing material Subsequently, the VOC gas molecule reacts with pre-adsorbed oxygen species on the surface of the sensor, and the electrons were released back to the conduction band (Eq (3.9)), resulting in an increase in surface electrons and conductivity and a decrease in resistance [43, 90] O2 (gas) → O2 (ads) (3.4) O2 (ads) + e- → O2- (3.5) O2 (ads) + 2e- → 2O- (3.6) O2 (ads) + 4e- → 2O2- (3.7) VOC (gas) → (3.8) VOC (ads) VOCs + nOx- → aCO2 + bH2O + ne- (3.9) The hollow structure of the Zn2SnO4 cubic and octahedron was beneficial for the total exposure of analytic gas on the outer and inner surfaces of the sensing material The hollow structure also enhanced the diffusion rate of gas molecules to the inside of the sensing material, thereby improving the sensing performance Recovery of the sensor was obtained after stop flowing analytic VOC gas, and again exposure to ambient air When the sensor was exposed to ambient air, oxygen molecules again adsorbed on the surface of the Zn2SnO4 cube and ionized to negatively charged surface-adsorbed oxygen species by capturing free electrons from the conducting band of the Zn2SnO4 cubic [52], as shown in Eqs 66 (3.4)–(3.7) As a result, the resistance of sensor recovers to the initial value after stop flowing analytic gas Figure 3.28 Schematic of the VOCs gas-sensing mechanism of the Zn2SnO4 67 CONCLUSIONS AND RECOMMENDATIONS Based on the results and analyses presented above, we have some conclusions: Successfully fabrication of Zn2SnO4 material with various structures of nanoparticles, hollow cubic, and hollow octahedron by hydrothermal method The obtained Zn2SnO4 materials had a uniformly hollow cubic and hollow octahedron structure with an average size of approximately µm and a wall thickness of about 150 nm formed from nanocrystals of around 28 nm Particularly for Zn2SnO4 nanoparticles, the average particle size is about 21 nm The gas sensing properties of Zn2SnO4 material with acetone, ethanol, methanol, NH3, H2, and CO were tested The results showed that the sensors ZTOP5_PH8 and ZTOP5_PH13 based on hollow cubic and hollow octahedron materials gave relatively good selectivity to VOCs The responses respectively, of ZTOP5_PH8 and ZTOP5_PH13 sensors to 125 ppm acetone were 34 and 44.52 times at the optimum working temperature of 450 °C The sensor's detection limit reaches 175 and 0.67 (ppb) We also explained the gas sensitivity mechanism of cubic and octahedron materials through the electron depletion region model The porous structure of hollow cubic and hollow octahedron enables gas diffusion, and thus enhance the gas sensing performance Although we have tried to make the research project as complete as possible, however, there are still many other issues that need to be addressed for further improvement Therefore, we have proposed further research directions, including: Continuing to study the effect of hydrothermal conditions on the formation of different structural morphologies of Zn2SnO4 materials, thereby elucidating the mechanism of material formation and simultaneously investigating the influence of light on the sensor parameters Study on denaturation of Zn2SnO4 material with some catalyst metals such as Pt, Pd, and Pt-Pd alloy or with some other metal oxides such as MoS2 to improve the gas-sensitive properties of the material With the remarkable advantages of Zn2SnO4 material, we expected to successfully develop a high-performance VOC sensor for 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assembled nanocrystal Zn2SnO4 for breath analysis", Sensors and Actuators A 302 (2020) 111834-111839 [IF2018: 2.73] Lai Van Duy, Nguyen Hong Hanh, Dang Ngoc Son, Pham Tien Hung, Chu Manh Hung*, Nguyen Van Duy, Nguyen Duc Hoa*, Nguyen Van Hieu, “Facile hydrothermal synthesis of two-dimensional porous ZnO nanosheets for highly sensitive ethanol sensor”, Journal of Nanomaterials 2019 (2019) 1-7 [IF2018: 2.23] Lai Van Duy, Nguyen Hong Hanh, Nguyen Duc Hoa+, Chu Manh Hung*, “Hydrothermal Synthesis of Zn2SnO4 Nanoparticles for Ethanol sensor”, Journal of Science & Technology 135 (2019) 067-071 Nguyen Hong Hanh, Lai Van Duy, Chu Manh Hung, Nguyen Van Duy, Nguyen Van Hieu, Nguyen Duc Hoa “Synthesis of octahedron Zn2SnO4 by hydrothermal method for high performance ethanol senser”, Vietnam Academy of Science and Technology, vol 58, No (2020) 78 ... tên tác giả luận văn: Lại Văn Duy Đề tài luận văn: Chế tạo vật liệu Zn2SnO4 cấu trúc nano ứng dụng cho cảm biến khí Chuyên ngành: Khoa học vật liệu- VLĐT Mã số SV: CA180178 Tác giả, Người hướng... PGS TS Nguyễn Phúc Dương ĐỀ TÀI LUẬN VĂN Chế tạo vật liệu Zn2SnO4 cấu trúc nano ứng dụng cho cảm biến khí Học viên: Lại Văn Duy Chuyên ngành: Khoa học vật liệu- VLĐT Giáo viên hướng dẫn (Ký ghi rõ... block for VOC gas sensor applications Therefore, this thesis targets to the ? ?Fabrication of Zn2SnO4 nanostructures for gas sensor application? ?? Aims of the thesis - To successfully fabricate Zn2SnO4