Preparation Of Spinel Structure Semiconductor Oxides And Their Gas-Sensing Properties

The gas sensing devices can be used to analyze specific gases in the environment qualitatively and quantitatively,realizing the conversion of chemical signals to directly measurable signals.It is widely used in environmental pollution gas detection,industrial/livelihood security,medical and health diagnosis,food safety.monitoring and many other fields.Semiconductor oxide gas sensors have always been a research hotspot in the sensor field because of their simple structure,high response value,better reliability,simple operation,easy integration and real-time monitoring of the gas to be measured.It is well known that the key to building high-performance gas sensors is the design and development of highly efficient semiconductor oxide sensitive materials.Compared with single oxides,the chemical composition and structure of multi-element metal oxide semiconductors are easier to control,which is beneficial to the construction of high-performance sensors.In this paper,the spinel structure binary metal oxide semiconductor is used as a sensitive material to improve the sensitive properties of binary metal oxide semiconductor by optimizing its microstructure and constructing heterostructure,and analyze its sensitive mechanism,including the following two parts of the experimental content:1.The ZnCr₂O₄ sensitive material with yolk-shell structure was prepared by one-step solvothermal reaction with zinc nitrate and chromium nitrate as zinc and chromium sources,and glycerol and isopropanol as reaction solvents.The characterization results of scanning electron microscopy（SEM）and transmission electron microscopy（TEM）characterization results show that the diameter of the ZnCr₂O₄ single microsphere is about 2.5μm,the thickness of the shell is about 0.5μm,and the size of the core is about1.25μm.The material is made into an indirectly heated sintered gas sensor and its gas sensitive characteristics are systematically tested.The test results show that the ZnCr₂O₄ sensor based on core-shell structure material has high selectivity for xylene gas,and the optimal working temperature is 225℃,the response value to 100 ppm xylene gas is as high as 200.7.In addition,the sensor maintained relatively stable gas-sensing properties during the continuous test for up to three weeks,which strongly shows that the yolk-shell structure-based ZnCr₂O₄ microspheres exhibit reliable long-term stability and repeatability.The excellent xylene sensing properties are attributed to the larger specific surface area of the core-shell structure,which can provide more active sites for the xylene gas molecules,and make the target gas molecules come into contact with the material and then conduct chemical reactions to a greater extent,resulting in improving the sensitivity of the device to xylene gas.2.Zn₂SnO₄ octahedral material was prepared by a one-step hydrothermal synthesis method,and NiO with different molar ratios were successfully loaded on the surface of the Zn₂SnO₄ material by subsequent wet impregnation.According to the characterization results of the scanning electron microscope and transmission electron microscope,the morphology of NiO/Zn₂SnO₄ composite materials does not change greatly compared with the matrix material,and they are still octahedral structures,but with the increase of NiO loading,the surface of sensitive material becomes rougher.The gas sensing test results show that the responses of all NiO/Zn₂SnO₄ composite oxides to 100 ppm acetone gas are higher than that of pure Zn₂SnO₄ octahedrons,and have better selectivity.Among them,the response of 3 mol%NiO/Zn₂SnO₄ composite material to 100 ppm acetone gas is as high as 49.8 at its optimum operating temperature of 300℃,which is nearly 4 times that of pure Zn₂SnO₄ material,and the response time is only 1 s.In addition,the sensor still responds with a response value of 1.4 to 100 ppb acetone gas,indicating that the 3 mol%NiO/Zn₂SnO₄ composite material possesses a low detection limit and can be used for trace detection of acetone gas.The reason for enhancing the gas sensing properties of the composite material is mainly due to the formation of a p-n heterojunction between the p-type semiconductor material NiO and the n-type semiconductor material Zn₂SnO_4,and the catalytic effect of NiO.