Porous ZnO Nanomaterials And Their Composite Structures Are Used In The Research Of Acetone Gas Sensing

With the development of industry,the life of people has become more and more convenient while the environment has been destroyed seriously day by day.The increasingly severe air pollution has been a great threat to people's physical health and living space.Therefore,it is important to realize real-time monitoring of toxic and harmful gases such as volatile organic gases in the environment.Gas sensor as an significant member of sensor family,could realize the quantitative detection or qualitative detection of gas,by changing the composition or concentration of gas into electrical signal.Nowdays,gas sensors have played the crucial role in industry,civil,environmental protection,medical and other fields.ZnO based gas sensor as a branch of metal oxide semiconductor sensor,has been a hot area of research since it was found in the last century,due to its low cost,easy to use,simple preparation and high sensitivity.However,the traditional ZnO based sensor has the disadvantages of low detection limit and poor selectivity.However,with the enhancement of people's environmental consciousness and health awareness,the traditional ZnO base sensor has been unable to meet people's needs in terms of minimum detection limit,selectivity and sensitivity.In this paper,the ZnO as a kind of wide-applied gas sensitive material is served as the research base,and the porous metal organic framework materials(MOF)are used as sacrifice templates to prepare a series of porous ZnO nanomaterial and its composite structures.The as-synthesized materials are used as sensing materials to prepare flat type gas sensors,and their gas sensing propertities are explored for low concentration acetone.Several factors that affect the sensing performance of ZnO based sensing materials are systematically discussed,including the nanostructure,metal oxide doping and precious metal doping.The main contents and results of this paper are as follows:(1)The microstructure has a great influence on the gas sensing perpformance of metal oxides.MOFs with high specific surface areas,open metal sites and well-defined pores,are the ideal self-sacrificial template for porous materials.In this paper,the ZIF-8 as a memerber of MOF with great chemical and thermal stablility and easy synthetic process,is used as the template to obtain ZnO nanomaterial by directly calcination.The as-prepared ZnO material has porous nanostructure and high specific surface area.The porous ZnO based sensor has great response to low concentration acetone and its sensitivity is 8.2 ppm-1 to lppm acetone at 275 ?.The ZnO based sensor also has good stability and selectivity towards acetone.It is investigated that porous structure and high specific surface,that supply rich exposure active parts and fast diffusion of gas,is the key for good sening properties of ZnO sensor.(2)The combination between metal oxide and metal oxide could further enhance the performance of a single materials through the synergistic effect of both materials.In this paper,ZIF-8 was used as the seed to obtain ZIF-8/ZIF-67 composites.The as-prepared ZIF-8/ZIF-67 composites are used as a template to obtain porous ZnO/Co3O4 composite.The gas sensing properties of porous ZnO/Co3O4 based sensor are studied,and the results are compared with the ZnO based sensor.The results show that the sensitivity of ZnO/Co3O4 towards 1 ppm acetone is 15.2 ppm-1 at 275 0C,which is higher than that of ZnO.Such enhacements could be attributed to the co-presence of several beneficial phenomenon:the higher specific area,more oxygen vacancy,p-n junction between ZnO and Co3O4 and the catalytic activity of Co3O4,(3)The metal oxide doping has been proved to be able to improve the gas sensing performance of the metal oxides.In this paper,gold nanoparticles with an average size of 5 nm are modified on the surface of ZIF-8 to obtain Au/ZIF-8 composites.The Au/ZIF-8 composites are then transformed into porous Au/ZnO composites by calcining in the air.The gas-sensing properties of porous Au/ZnO based sensor are tested and the results are compared with pure ZnO.The experiments demenstrat that the Au/ZnO sensor show enhanced gas properties compepared with ZnO sensor.The sensitivity of Au/ZnO towards 1 ppm acetone is 17.1 ppm-1,and its response and recovery speed are improved.The improvements of gas sensing performance are mainly attributed to the doping of Au nanoparticles.Au nanoparticles with electronic and chemical sensitization,could increase the oxygen adsorption quantity of ZnO,facilitate chemical reaction and thicken the electronic depletion layer.This paper aims at the defects of traditional ZnO materials,investing the effective approaches to improve the sensing performance of ZnO materials throuth simple MOF route.Several factors that affect the sensing performance of ZnO are explored,including the nanostructure,metal oxide doping and precious metal doping.The ZnO nanomaterial and its composits are obtained with great gas-sensing performance through simple synthetic process,which proves porous metal oxide and its composite through MOF template route has wide application prospect in the field of gas sensor.