Construct Of Hierarchically Porous Nanostructured ZnO And Study Of Its Gas-sensing Properties

ZnO is a kind of typical n-type semiconductor material with direct and wide band gap.For its nanomaterials having both semiconductor features and unique optical,electrical,magnetic and thermal properties,ZnO has been widely used as transparent conductive film,transistor,ceramics,catalyst and gas sensors.Therefore,the synthesis and research of performances of nano-structured ZnO have become research hotspot in many fields.This paper focuses on constructing ZnO nanomaterial with hierarchically porous structure and the research of its gas-sensing performances.Porous ZnO was successfully constructed by a time-saving,simple and practical solution combustion synthesis(SCS)method without using template.It is easy to introduce dopant and compound during combustion process,in order to obtain gas-sensing materials which are sensitive to volatile organic compounds(VOCs)and inflammable gases.What's more,the gas-sensing performances of ZnO and its composites-based gas sensors towards n-butanol,butane and formaldehyde were mainly studied.Effect of structure and composition of porous ZnO nanomaterials was also discussed.Specific contents are as follows:(1)Synthesis and characterization of ZnO,AZO(Al-doping ZnO),Ag/AZO,Pt/AZO and Ag/ZnO hierarchically porous nanomaterialsZnO,AZO,Ag/AZO,Pt/AZO and Ag/ZnO hierarchically porous nanomaterials were successfully constructed through solution combustion synthesis(SCS)method.XRD,SEM,TEM,XPS and BET characterization methods were used to obtain the information of their crystal structure,composition,morphology characteristics,surface chemistry,pore structure and specific surface area,respectivily.The results show that it is easy to build porous ZnO,AZO,Ag/AZO,Pt/AZO and Ag/ZnO with high purity,good crystalline and large specific surface area.They all have wide pore radius distribution,including through holes of micropores,misopores and macropores,which provide large adsorption and reaction surface for O2 and objective gases.Preparation process and characterization results indicate that construction of porous nanomaterial is mainly related to oxidant,reductant and combustion agent in reactant.Besides,the formation of porous morphology is assigned to release of N2,CO2 and H2O during combustion process.(2)Gas-sensing properties of ZnO,Ag/ZnO,AZO,Ag/AZO and Pt/AZO based gas sensorsThe resistance type semiconductor gas sensors were fabricated after grinding,coating,drying,sintering,welding and aging process,and their gas-sensing performances were tested on a WS-30A system.The results indicate that 5%Pt/AZO and 1%Ag/ZnO based gas sensors are sensitive to butane and formaldehyde,respectively,and their optimum working temperature is 200? and 240?,respectively;ZnO,2.5%AZO and 2.5%Ag/AZO based gas sensors are sensitive to n-butanol,and their optimum working temperature is 300?,300? and 240?,respectively.These gas sensors show good selectivity,repeatability and fast response-recovery rate in detecting n-butanol,butane and formaldehyde.It takes a period of time to become stable.Considering the information of component,morphology,specific surface area and surface statement of ZnO,AZO,Ag/AZO,Pt/AZO and Ag/ZnO,enhanced gas-sensing performances can be mostly attributed to a large number of free electrons introduced by A1 dopant,and the metal-metal oxide heterojunction,like Ag-AZO,Pt-AZO and Ag-ZnO.