Preparation And Gas Sensing Properties Of ZIF-8 Coated SnO₂ Based Composite Nanofibers

Industrial civilization has brought mankind a rich material life,but also increased the depletion of the earth's resources and environmental pollution.There is an urgent need to monitor flammable,explosive and toxic gases in air,living and production premises to protect people and property.Metal oxide semiconductor gas-sensing materials such as SnO₂ and ZnO are widely used because of their low cost,simple preparation,high sensitivity and fast response.However,problems such as high operating temperature,poor selectivity and high influence by ambient humidity have also become key factors limiting their further application.In recent years,as a typical Metal-Organic Frameworks,Zeolitic Imidazolate Frameworks(ZIF-8)with Zn as the node has been gradually introduced into the field of sensors.In this paper,the preparation and gas sensing properties of ZIF-8 coated SnO₂ based nanofibers were studied using a self-sacrificing template strategy,and the effect of ambient humidity on the gas sensing properties of the composite nanofibers was discussed.The SnO₂ based nanofibers were also doped with rare earth elements Er to further improve the gas sensing properties of the composite nanofibers,the main research work is as follows:1.SnO₂ nanofibers were prepared by electrospinning.The crystal structure and morphology of the nanofibers were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM)and specific surface area analyzer(BET).The results show that rutile structured SnO₂ nanofibers with uniform morphology were obtained.The gas sensing test shows that the SnO₂ nanofibers are most sensitive to H₂S.The optimum working temperature is 250?,its sensitivity to 5 ppm H₂S gas is 9.9 at 55%relative humidity,and the detection limit is 1 ppm.However,ambient humidity has a significant effect on the gas sensing properties of SnO₂ nanofibers,which are poorly resistant to moisture.2.Combining electrospinning and hydrothermal methods,ZIF-8 coated SnO₂based composite nanofibers with core-shell structure were prepared using SnO₂/ZnO nanofibers as a template and Zn²⁺source.The effects of Sn/Zn and coating time on the gas sensing properties of the composite nanofibers were studied.It is found that the amount of Sn/Zn and coating time has an obvious effect on the gas sensing properties of the composite nanofibers.When the Sn/Zn ratio is 2/1 and the coating time is 15 h,the composite nanofibers show the best gas sensing properties.Its sensitivity to 5 ppm H₂S is 358.0 at an optimum operating temperature of 200°C(55%relative humidity)and maintains 81.3%at relative humidity of 90%,indicating that the ZIF-8 coating significantly suppresses the adverse effects of ambient humidity on the gas sensing properties of the composite nanofibers.The lowest detection limit was decreased to0.03 ppm.3.In order to further improve the gas sensing properties of SnO₂/ZnO@ZIF-8composite nanofibers,the rare earth element Er was used to doping SnO₂/ZnO nanofibers.The effects of Er doping on the microstructure and gas sensing properties of SnO₂/ZnO@ZIF-8 composite nanofibers were studied.The results show that a small amount of Er doping has no obvious effect on the morphology and crystal structure of nanofibers.The gas sensing test shows that Er doping can decrease the working temperature of composite nanofibers and improve the gas sensing properties.The sensitivity of 3 at%Er doped SnO₂/ZnO@ZIF-8 composite nanofibers to 5 ppm H₂S is3979.0(25%relative humidity).At 90%relative humidity,the sensitivity to 3 ppm H₂S(55%relative humidity)can maintain 84.2%,and still respond to 0.03 ppm H₂S.