Study On The Preparation And Performance Of Metal Oxide Based Gas Sensitive Materials

As gas sensors in Internet of Things and miniature health detectors have provided great convenience to human lives,high operating temperature is one of significant shortcomings for gas sensor,which has become more and more obvious.The development of low operating temperature gas sensors is one of key factors driving its rapid development.Therefore,it is significance to develop high performance gas sensors at low operation temperature.Sensitive materials play an important role in gas-sensitive performance.Choosing appropriate sensitive materials contribute to improve the performance of gas sensor.Metal oxide-based sensors have the advantages of high sensitivity,long life and low cost.Such materials have the potential to develop into high-performance devices and become a research hotspot.However,there still three important problems with metal oxide-based sensors:(1)The operating temperature of a single metal oxide gas-sensitive material is relatively high;(2)The selectivity of this type of material is relatively poor during detection;(3)In the atmosphere,vary of humidity possesses an important impact on the performance of such sensing material.Heterojunction is an important way to improve sensor performance and optimize operating temperature.As the third type of semiconductor,GaN possesses high electron mobility,excellent chemical stability,and easily forming heterojunction,which provides high-quality materials for the development of high-performance metal oxide-based gas sensors at low-temperature.This thesis is based on metal oxide nanomaterials to design gas-sensitive materials with heterojunctions,for solving the key problems of metal oxide-based gas sensors and gradually achieving low operating temperature.The main research contents of this article are as follows.1.Porous GaN-based layered heterojunction is applied to the humidity sensor.Hexagonal zinc oxide nanosheets(ZnO)are prepared the by hydrothermal method.Then ZnO/PGAN heterojunction was prepared by spraying method and used to sensing material of the humidity sensor.The sensitivity of ZnO/PGAN based humidity sensor is 161.0 in the relative humidity range of 12%-96%.Meanwhile,the response time is 7 s and the recovery time is 13 s.The response mechanism of water molecules on the surface of ZnO/PGAN is described.2.Electrodeposition in-situ preparation technology is applied for fabricated ZnO with different morphologies on the surface of gallium nitride by controlling the deposition voltage and time,and in-situ preparation of ZnO/GaN layered heterojunction.Constructing a two-dimensional ZnO/GaN gas sensor with a concentration of 50 ppm H2S,the sensor can achieve a response time of 82 s and a recovery time of 48 s at 240?,while the detection line is reduced to 1 ppm.At room temperature,the response and recovery time of 3D flower-like ZnO/GaN based gas sensor to organic volatiles(50 ppm ethanol)is 12 s and 9 s,respectively.Meanwhile,the minimum detection line of 3D flower-like ZnO/GaN based gas sensor is reduced to 100 ppb.Conclusion and detailed discussion of the response mechanism of ZnO GaN layered heterojunction.3.In-situ hydrothermal method is used to prepare internal heterojunction of ZnO/GONR.The composite material has a hierarchical porous structure.In the NO2 concentration range of 1 ppm-50 ppm,the sensitivity of ZnO/GONR based sensor dispalys an excellent linear relationship with concentrations of NO2 at room temperature.In addition,the sensitivity of NO2 exceeds that of compared gases,such as ozone,acetic acid,ethanol,methanol,formaldehyde and so on.Therefore,the gas sensor exhibite excellent selectivity to NO2.4.In addition to ZnO-based heterojunctions,other metal oxides have also been studied.The flexible core-shell structure heterojunction is applied to the gas sensor.The core-shell CNTF/NiO heterojunction is prepared on the flexible CNTF by in-situ hydrothermal method.At room temperature,the sensitivity of CNTF/NiO-based sensors to 50 ppm H2S is 35.2.At the same time,the sensing material is bent at any angle of 180°.However,the gas response change is 1.2%after 600 bends.