Research On Gas Sensitivity Of ZnO-based Heterojunction Sensor To Acetone And Xylene

In recent years,as air quality has declined,the quality of food and drugs has deteriorated,and people’s safety awareness has increased,monitoring various toxic,harmful,flammable and explosive gases in life and production places has become imminent,and its detection range has been applied to industry,food safety,public safety,indoor pollution,and medical diagnosis.Among many gas sensors,metal oxide semiconductor gas sensors has been well developed to monitor toxic gases due to their small size and low cost.ZnO is an n-type semiconductor.Because of its high chemical stability and high electron mobility,it has shown potential application prospects in the field of metal oxide semiconductor gas sensors.However,the sensor based on pure ZnO has the disadvantages of poor selectivity and low sensitivity,which limits its practical application.In this paper,the pure ZnO material is modified by constructing a p-n heterojunction,a ZnO-based gas sensor with high selection and high sensitivity is designed and synthesized,and its sensitivity enhancement mechanism is clarified.（1）ZnO nanorods and ZnO nanoflower sensors are prepared by hydrothermal method and co-precipitation method,respectively.The purity of the synthesized materials are proved by X-ray diffraction.Scanning electron microscopy observs that the length of ZnO nanorods are 4-15μm,while ZnO nanoflowers are composed of nanorods with a length of about 2μm,and their particle size is smaller,with a diameter of about 4-5μm.The gas sensing test results show that the response value of ZnO nanoflower gas sensor to 100ppm acetone at 292 ^oC is 10.3,which is higher than the response value of ZnO nanorods gas sensor（5.24）.（2）The p-Co₃O₄/n-ZnO nanoflower heterojunction is constructed by the impregnation method,and the structure and performance characteristics of the Co₃O₄ heterojunction with different contents are studied by different characterization methods.According to the gas sensor performance test,the best modification amount of Co₃O₄is 0.9 wt%.Under the optimal modification amount,the sensor shows a higher response value（89）and selectivity to acetone than the ZnO nanoflower sensor,and also shows better linearity and fast response recovery speed（10 s/23 s）.The mechanism of heterojunction sensitization is the p-n heterojunction effect and the catalytic effect of Co₃O₄.（3）In order to further verify the sensitization mechanism of heterojunction,the n-ZnO nanoflowers modified with p-NiO nanoislands are successfully synthesized by dipping method and annealing treatment.For this,the gas performance of the sensor based on NiO/ZnO composites is controlled through the change of catalytic activity via NiO loading.Compared with pure ZnO sensors,NiO/ZnO sensors show unique selectivity and fast response time（1 s）to xylene.The sensor’s response to 100 ppm xylene is 53,which is3.3 times that of the ZnO nanoflower sensor.It is verified that the above-mentioned sensitization mechanism.The heterojunction effect and the catalytic effect of NiO are the main reasons for the improvement of material performance.