Preparation Of Zinc Oxide Matrix Composites And Its Sensing Properties Study

As a typical n-type metal oxide semiconductor,ZnO has been widely investigated due toits great potential in the gas sensing field.ZnO based gas sensors have played an important role in the detection of VOC_S such as benzene,acetone and ethanol.However,simple block ZnO as a sensing material still has some disadvantages such as insufficient sensitivity,long response/recovery time and cross response,which greatly restricts the wide application.It is an effective strategy to improve the gas sensitive performance of ZnO based gas sensor by adjusting the morphology and structure,hetero-atom and noble metal loading.In this paper,ZnO nanomaterials with different morphologies were synthesized by thermal solvent method.On this basis,further functionalization was carried out to obtain excellent sensing performance.The main research content consists of the following three parts:(1)ZnO/Co₃O₄ porous nanosheets were successfully developed via modulating the proportions in p-n heterojunction composites by a hydrothermal method.The as-synthesized materials were applied to fabricate sensors to study their gas sensing performance.The response value(S=Ra/Rg)of the ZnO/Co₃O₄ sensor is calculated to be 67.8 for 50 ppm triethylamine,which is much better than that of as-prepared pristine ZnO.Interestingly,the ZnO/Co₃O₄ sensor also exhibits a high response to triethylamine even in high humidity(77%).In order to further explore the sensitization reason of composite materials,the prepared samples were characterized by BET,TEM and XRD,and the possible sensing mechanism was discussed.Our work provides a strategy to fast probe triethylamine via design of p-n heterojunction ZnO/Co₃O₄ sensors.(2)In this work,different content of Ce doped ZnO porous nanosheets were successfully synthesized via a facile and controllable hydrothermal method and their sensing properties were investigated.1 at%Ce doped ZnO(CZO-1)sensor exhibited a high response(S=15.1for 100 ppm aniline),and excellent selectivity toward aniline against other gases at room temperature compared with pristine ZnO.The abundant oxygen vacancies(O_V),high specific surface area and the interface interaction between of Ce O₂ and ZnO effectively enlarged the resistance variation due to the change in oxygen adsorption.The two-dimensional(2D)porous structure also plays an important role in the excellent sensing performance due to the excellent electron transport capability and abundant gas diffusion channels.DFT study results indicated the interaction between ZnO and aniline could be enhanced by introducing O_Vand Ce doping.Thus,this work indicated that the CZO composites could be a potential candidate for aniline detection at room temperature.(3)The development of high sensitivity acetone gas sensor is of great significance for air quality detection and medical diagnosis.Herein,ZIF-8 derived ZnO/Ce O₂ heterojunction was prepared by simple hydrothermal method to realize ppb level detection of acetone.ZnO was compacted on the surface of Ce O₂ material using ZIF-8 as sacrificial template,which was beneficial to enlarge the specific surface area,form heterogeneous interface and generate abundant oxygen vacancies.ZnO@Ce O₂-1min composites show excellent gas sensitive property for acetone,with low detection limit(240 ppb),high response(32/100 ppm),high selectivity and good stability.The synergistic effect of ZnO@Ce O₂ heterojunction and oxygen vacancy is responsible for the enhancement of composites gas sensitivity.The resistance variation of the ZnO@Ce O₂ heterojunction enlarges the resistance modulation,and the oxygen vacancy increases the free charge concentration in the material to provide more active sites.Therefore,the successful synthesis of ZnO@Ce O₂ composites provides important insights and strategies for the design of ppb acetone gas sensitive materials.