| In this thesis, the graphene-metal oxide composite gas sensing materials and the gas sensing properties of graphene-Zn2SnO4, graphene-SnO2, graphene-mixed In2O3-SnO, and graphene-Sb-SnO2 are reviewed detailed.In chapter one, the types and evaluation of the gas-sensing material are introduced in detail; the structures and properties, common preparation methods, characterization methods, functionalization, and applications of graphene are introduced in detail; the preparation methods and applications in gas sensors of graphene-metal oxide are also introduced in detail.In chapter two, graphene-Zn2SnO4 composites(G-Zn2SnO4) with different graphene content are prepared by hydrothermal method. The G-Zn2SnO4 composites are characterized by Fourier transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD), Scanning electron microscopy(SEM), and Raman spectrum, respectively. The effect of graphene content and the hydrothermal temperature on the gas sensing properties of G-Zn2SnO4 composite materials is studied. The gas sensing properties of the G-Zn2SnO4 composite materials are investigated. The results reveal that when the operating temperature of 0.5 wt%G-Zn2SnO4(200°C, 24 h) sensor is 20°C, the response of 0.5 wt%G-Zn2SnO4(200°C, 24 h) sensor to 1000 ppm formaldehyde vapor is 18.9, which is the maximum value, the response time and recovery time for 1000 ppm formaldehyde vapor are 200 s and 50 s, respectively; the minimum detection limit of the sensor based on 0.5 wt%G-Zn2SnO4(200°C, 24 h) composite to formaldehyde vapor is 10 ppm, the response of the sensor based on 0.5 wt%G-Zn2SnO4(200°C, 24 h) composite to 10 ppm formaldehyde vapor attains 1.1, the response time and recovery time for 10 ppm formaldehyde vapor are 50 s and 50 s, respectively. When the operating temperature of 0.5 wt%G-Zn2SnO4(200°C, 24 h) sensor is 20°C, the stability of 0.5 wt%G-Zn2SnO4(200°C, 24 h) sensor to 1000 ppm formaldehyde is poor.In chapter three, graphene-SnO2(G-SnO2) composites are prepared by hydrothermal method. The effect of graphene content and the hydrothermal temperature on the gas sensing properties of G-SnO2 composite materials is studied. The gas sensing properties of SnO2 sensor and 0.1 wt%G-SnO2(100°C, 10 h) sensor to formaldehyde, ethanol, acetone, benzene, acetic acid and ammonia are also studied. The results reveal that the sensor based on 0.1 wt%G-SnO2(100°C, 10 h) exhibits high responses to dilute formaldehyde and ethanol. When the operating temperature of 0.1 wt%G-SnO2(100°C, 10 h) sensor is 89°C, the response of 0.1 wt%G-SnO2(100°C, 10 h) sensor to 1000 ppm formaldehyde is 13.6, the response time and recovery time for 1000 ppm formaldehyde are 44 and 170 s, respectively; the response of 0.1 wt%G-SnO2(100°C, 10 h) sensor to 0.1ppm formaldehyde attains 1.2; when the operating temperature of 0.1 wt%G-SnO2(100°C, 10 h) sensor is 165°C, the response of the sensor based on 0.1 wt%G-SnO2(100°C, 10 h) to 1000 ppm ethanol is 11, the response time and recovery time for 1000 ppm ethanol are 14 and 28 s, respectively; the response of 0.1 wt%G-SnO2(100°C, 10 h) sensor to 0.1 ppm ethanol attains 1.1.In chapter four, graphene-mixed In2O3-SnO(G-In2O3-SnO) composites are prepared via hydrothermal method. The gas sensing experiments include the effects of graphene content and In2O3 content on the gas-sensing properties of G-In2O3-SnO to formaldehyde vapor, the selectivity, the stability, and the responses of the sensor based on 0.1 wt%G-In2O3-SnO composite to formaldehyde vapor in various concentrations. The experimental results reveal that the sensor based on 0.1 wt%G-In2O3-SnO composite(the mole ratio of In2O3/SnO is 1:9) exhibits high response to formaldehyde vapor. When the operating temperature is 200°C, the response of 0.1 wt%G-In2O3-SnO(the mole ratio of In2O3/SnO is 1:9) composite sensor to 1000 ppm formaldehyde vapor is 238, the response time and recovery time for 1000 ppm formaldehyde vapor are 52 and 55 s, respectively; the response of the sensors based on 0.1 wt%G-In2O3-SnO(the mole ratio of In2O3/SnO is 1:9) composite to 0.01 ppm formaldehyde vapor attains 1.2, and the response time and the recovery time for 0.01 ppm formaldehyde are 4.5 and 5.4 s, respectively. When the operating temperature is 200°C, the stability of the sensor based on 0.1 wt%G-In2O3-SnO(the mole ratio of In2O3/SnO is 1:9) composite to 1000 ppm formaldehyde vapor is poor.In chapter five, graphene-Sb-SnO2(G-Sb-SnO2) composites are prepared via hydrothermal method. The effect of graphene content and Sb content on the gas sensing properties of G-Sb-SnO2 composite materials to acetaldehyde vapor is studied. The gas sensing properties of the G-Sb-SnO2 composite materials are investigated. The experimental results reveal that the gas sensing properties of Sb-SnO2 to acetaldehyde vapor is significantly enhanced and the optimum operating temperature of Sb-SnO2 sensor is decreased by doping different content of graphene. When the operating temperature is 20°C, the response of the sensor based on 0.1 wt%G-Sb-SnO2(the mole ratio of Sb/SnO2 is 1:9) composite to 1000 ppm acetaldehyde vapor is 64.5, the response time and recovery time for 1000 ppm acetaldehyde vapor are 24 and 12 s, respectively; the response of the sensor based on 0.1 wt%G-Sb-SnO2(the mole ratio of Sb/SnO2 is 1:9)composite to 0.1 ppm acetaldehyde vapor attains 1.4, and the response time and the recovery time for 0.1 ppm acetaldehyde are 2 and 8 s, respectively. When the operating temperature is 20°C, the stability of the sensor based on 0.1 wt%G-Sb-SnO2(the mole ratio of Sb/SnO2 is 1:9) composite to 1000 ppm acetaldehyde vapor is poor. |
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