Preparation Of Perovskite-type Composite Metal Oxide Nanomaterials And Their Gas Sensing Properties

In this era when everything is interconnected,although technology has brought great convenience to people's lives,the accompanying air pollution problems cannot be underestimated.At present,the majority of air pollutants come from chemical production and automobile exhaust,and a small part from the volatile organic compound vapor produced by indoor decoration.Volatile organic compounds?VOCs?always surround our lives,which seriously affect people's health.In order to prevent and control the leakage of volatile organic compound vapor timely and efficiently,metal oxide semiconductor gas sensors with their simple manufacturing process,excellent gas sensitivity and low cost requirements have become a research focus of researchers,and have been widely used in daily life.However,although metal oxide semiconductor gas sensors have many superior performance,their poor selectivity,high operating temperature,long response/recovery time and other problems are still the key points that need to be improved.In this paper,aiming at the above three problems,the low-cost perovskite-type composite metal oxides were used as sensitive materials to prepare gas sensors to test their gas sensing performance.The main research work of this paper is as follows:?1?Porous Ag-modified ZnSnO₃ hollow nanocubes were synthesized by a solvothermal method and a deposition strategy.It was found that ZnSnO₃ had an amorphous crystal structure through characterization.Therefore,the material not only possessed a large specific surface area,but also had a large quantity of active dangling bonds on the surface.The uniform modification of Ag nanoparticles further increased the catalytic active sites on the surface.In order to explore its gas sensing performance,the prepared materials were fabricated into gas sensors for performance testing.By comparing the gas sensing properties of pure ZnSnO₃ and ZnSnO₃modified with different Ag content,it could be found that appropriate amount of Ag modification can effectively improve the gas sensing properties of pure ZnSnO₃.Especially the response of the sensor based on 0.6 at%Ag-functionalized ZnSnO₃ to100 ppm acetone was as high as 31.62,and the detection limit was 1 ppm.In addition,the sensor also possessed ultra-fast response/recovery process?2 s/3 s?and outstanding selectivity for acetone.Since Ag nanoparticles can effectively promote the dissociation of oxygen and increase the amount of chemisorbed oxygen on the surface of the materials,the appropriate introduction of Ag particles will be an effective means to improve the gas sensing properties of pure materials.?2?Different amount of PrFeO₃ modified?-Fe₂O₃ core-shell nano-octahedrons were synthesized by a hydrothermal route and a deposition method,and corresponding gas sensors were prepared to test their gas sensing properties.Because the materials possessed good gas permeability and large specific surface area,it could provide more adsorption sites for oxygen and target gas,so the PrFeO₃/?-Fe₂O₃composite material showed excellent gas sensing properties.Compared with pure?-Fe₂O₃,PrFeO₃/?-Fe₂O₃ composites had lower optimum operating temperature and better selectivity to ethyl acetate.Besides,the response of the sensor based on PrFeO₃/?-Fe₂O₃ composite to 100 ppm ethyl acetate was as high as 22.85,and the response and recovery time was 8 s and 9 s.The introduction of PrFeO₃ increased the basic sites on the surface of?-Fe₂O₃ and enhanced the concentration of oxygen ions on the surface of?-Fe₂O₃,which further improved the response of the materials to ethyl acetate.In addition,the combination of PrFeO₃ and?-Fe₂O₃ to form a p-n heterostructure to expand the range of sensor resistance signals can also significantly improve its gas sensing performance.?3?CdS quantum dots modified CdSnO₃ porous nanocubes were prepared by simple hydrothermal and precipitation methods,and fabricated into gas sensors to explore gas sensing properties of the materials.CdSnO₃ was an amorphous crystal structure with active dangling bonds on its surface.CdS quantum dots had a large surface to volume ratio,and the surface modification by CdS quantum dots significantly expanded the specific surface area of CdSnO₃ and increased the adsorption sites on the surface of materials.The optimum operating temperature of the sensor based on CdS quantum dots modified CdSnO₃ porous nanocubes was138°C,the response of the sensor to 100 ppm isopropanol was 20.12,and the response time and recovery time were both 10 s.In addition,the CdS-modified CdSnO₃ porous nanocubes had a detection limit of 1 ppm for isopropanol,while that of pure CdSnO₃ was 5 ppm.The introduction of CdS quantum dots can effectively expand the specific surface area of the pure material and increase the adsorption sites on the surface of the material to improve its response.Therefore,modifying pure materials with CdS quantum dots will also become a candidate method to improve the performance of gas sensors.Three different perovskite-type metal oxides were prepared by hydrothermal method and water bath method,and gas sensors were prepared to test their gas sensing performance.The results showed that gas sensors based on perovskite-type metal oxides had fast response recovery speed and low operating temperature.In addition,noble metal nanoparticles,metal oxides and quantum dot materials were introduced to modify the surface of the above materials.After the proper surface modification,the performance of the gas sensors had been significantly improved.