Study On Preparation And Gas Sensing Performances Of ZnO-based Composites

In order to develop high-performance gas sensors,it is important to find suitable gas sensing materials with high sensitivity,selectivity and stability.Among them,Zinc oxide(ZnO),as a typical n-type metal oxide semiconductor with high thermal and chemical stability,low cost and high conductivity,has been widely used in the study of various combustible and harmful gases.However,the traditional ZnO gas sensors still face certain challenges in terms of low concentration detection,high selectivity,fast response,and high reliability.This paper takes ZnO semiconductor as the basic material,and improves the gas sensing performance of ZnO monomer material by doping rare earth elements and constructing p-n heterojunction with p-type transition metal oxides.And studies the reasons for improving the gas sensitivity of ZnO matrix material by doping and p-n heteropair.The main research contents of this paper are as follows:(1)Pure ZnO and Ce-doped ZnO porous micro flower-like composites with different molar fractions of Ce were successfully prepared by hydrothermal method.The microstructure,morphological characteristics and composition information were examined by means of X-ray diffractometer,field emission scanning electron microscopy,and X-ray photoelectron spectroscopy.The ethanol gas sensing properties were systematically investigated between the pure ZnO and Ce-doped ZnO materials with different molar fractions.The results indicate that Ce doping can improve the performance of ZnO sensor.Especially,the ZnO doped with 1.2 at%Ce exhibited the highest response to 100ppm ethanol at the operating temperature of 300?,and the response value was about 59.9,which was 6.1 times higher than that of the pure ZnO sensor.XPS results show that the doping of Ce has a great influence on the distribution of oxygen,which obviously increases the proportions of oxygen vacancy and chemisorbed oxygen species,thereby greatly improving the response value of the sensor.It can be known from the gas sensing performance test that the 1.2at%Ce/ZnO sensor exhibits higher response,relatively lower operating temperature,fast response/recovery characteristics,good repeatability and stability.(2)Pure ZnO and micro flower-like NiO/ZnO p-n heterojunction composites with different NiO contents were successfully synthesized by using a facile one-step hydrothermal process.The microstructure,morphological characteristics and composition information were examined by means of XRD,SEM,and XPS.The effects of different NiO content on the structure,morphology,and gas sensitive properties of micro flower-like NiO/ZnO composites were systematically investigated.The results show that NiO/ZnO microflower sensor exhibited the enhanced response to formaldehyde and lower operating temperature compared to pure one.Especially,the NiO-3/ZnO microflower sensor has a response value of 21.3,which was 6.7 times higher than that of the pure one.In add ition,the sensor has the characteristics of relatively low operating temperature,fast response/recovery,good reproducibility and stability.The enhanced sensing properties were probably attributed to the formation of p-n heterojunctions at interface and the catalytic effect of NiO,which significantly enlarges surface depletion region and increases potential barrier.