| NO2,as an atmospheric pollutant,is one of the main causes of smog,acid rain,photochemical smog,and the greenhouse effect.This pollutant gas has a bad effect on human health and sustainable development.Therefore,the development of a high-performance gas sensing material to detect NO2 is particularly important for improving air quality and ensuring sustainable social development.As a semiconductor with wide bandgap,low resistance,and high thermal stability,In2O3 has already shown a good application prospect in the application of harmful gas detection.However,In2O3 has some defects,such as high operating temperature,long response and recovery time,and poor selectivity,which restricts its further development.In this thesis,oxygen defect self-doping and second-phase modification are used to further improve the gas sensing performance of In2O3.First,a composite soft template method was used to prepare an In(OH)3 precursor suspension with a hollow sphere structure.A hollow In2O3 gas sensing coating with a high specific surface area and rich in oxygen defects were prepared by subsequent plasma spraying.Second,CuO nanoparticles-loaded In2O3 hollow sphere composite gas sensing coatings and ZnO nanoparticles-loaded In2O3 hollow sphere composite gas sensing coatings were prepared by the second phase modification.The structure characterization and gas sensing performance test were performed.Finally,the mechanism of sensing performance improvement was analyzed.The specific research content is as follows:(1)An In(OH)3 precursor suspension with a hollow spherical appearance and a more stable structure was prepared by an improved composite soft template method.The H2 flow rate of plasma forming gas was used as a variable to prepare a hollow structure In2O3 gas sensing coating rich in oxygen defects.The optimal working temperature of the gas sensors prepared with three different H2 flows rates is 100?.When the H2 flow is 2 L/min,the coating has the best gas sensitivity to NO2,the response value to 100 ppb NO2 reaches 4.7,response/recovery time is only 475/770 s,and has good stability.When the H2 flow rate is 2 L/min,the gas sensing coating is rich in the oxygen defects,thereby having good gas sensing performance.When the H2 flow rate is 4 L/min,the oxygen defect content is the highest,but the hollow ball structure is destroyed by high-temperature and high-speed plasma flame,and the specific surface area is greatly reduced,so the gas sensing performance is sharply reduced.(2)Cu(NO3)3 solutions with different atomic ratios were added to the In(OH)3 precursor suspension.CuO-In2O3 hollow sphere composite gas sensing coatings were prepared by a high-temperature reduction method.Five composite gas sensing coatings with different atomic ratios were obtained.The best working temperature of the five groups of gas sensors is 100?.When the CuO atomic ratio is 2%,the sensor has the best gas sensitivity performance to NO2,and the response value to 500 ppb NO2 reaches 859.The response/recovery time is only 430/170 s with excellent selectivity.The proper loading of CuO nanoparticles greatly improves the sensitivity of In2O3 based gas sensors and reduces the response/recovery time.It is considered that the p-n heterojunction formed between CuO and In2O3 is the main reason for the improvement of gas sensing performance.(3)ZnSO4 solutions with different atomic ratios were added to the In(OH)3 precursor suspension,and ZnO-In2O3 hollow sphere composite gas sensing coatings were prepared by a high-temperature reduction method.The best working temperature of the five groups of gas sensors is 75?.Among these five groups of sensors,when the ZnO atomic ratio is 1%,the gas sensor has the best gas sensitivity performance to NO2,and the response value to 500 ppb NO2 reaches 2412.The response/recovery time is only 370/135 s,and it has good stability and selectivity.It is considered that the heterojunction formed between ZnO and In2O3 and the adhesion of ZnO nanoparticles increase the specific surface area of the material,which are the main reasons for the improvement of gas sensing performance. |
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