| With the development of industrialization,the amount of volatile organic solvents increased gradually.Volatile organic gas(VOCs)is not only easy to cause respiratory diseases,but also cause safety accidents.Metal oxide semiconductor gas sensors have the advantages of simple structure,low cost and high sensitivity,and have been widely studied and applied in the field of detecting organic volatile gases.Among them,ZnO is one of the earliest and most widely used gas-sensitive materials.Due to the complexity of the use environment,ZnO gas sensors still have the problems of poor selectivity,high optimum use temperature and narrow detection limit.Through the systematic study of the influence law of material structure and composition on ZnO gas sensing performance,the mechanism of gas sensing of ZnO based sensitive materials is analyzed,and the effective method to improve the ZnO based gas sensor is explored,which is of great significance for improving environmental detection capabilities and ensuring production safety.In this paper,the porous ZnO ultrathin nanosheet,In2O3/ZnO and Zn2SnO4/ZnO heterostructures were synthesized by hydrothermal,sol-gel,and chemical precipitation methods.The gas sensing performance of ZnO based gas sensors was improved by structural design and composition regulation,and gas sensing mechanism was analyzed.The specific tasks is as follows:The porous ZnO ultrathin nanosheets have been prepared by heat treatment of the precursor,which was synthesized by hydrothermal method with GO as template,zinc nitrate as main material and methenamine as precipitant.XRD?SEM?TEM was used to characterize the crystal structure and microstructure of the product to study the effect of GO on the structure and morphology of the product.The gas sensing performance test results showed that the sensitivity of porous ZnO ultrathin nanosheets to 100 ppm acetylacetone at 340? was 191.1,about 4 times that of the ZnO nanoclusters without GO,and response-recovery times were 19 s and 94 s,respectively.EPR,PL,Raman and other methods were used to further analyze the porous ZnO ultrathin nanosheets and elucidated its gas-sensitive mechanism.Studies have shown that the specific surface area of the porous ZnO ultrathin nanosheets was 130.5 m2/g,and the large specific surface area provided a large number of active sites for gas-sensitive reactions.In addition,its surface has a large number of oxygen vacancies,and the abundant oxygen vacancies promote the adsorption and ionization process of oxygen molecules and reduced the band gap,thus improving the gas sensitivity performance.ZnO nanorods were prepared by the sol-gel method using zinc acetate as the main raw material and polyvinylpyrrolidone(PVP)as the surfactant.The In2O3/ZnO heterojunction composite was prepared by calcining the precursor at high temperature,which was synthesized by chemical precipitation with ZnO nanorods as matrix,indium nitrate as modification material and ammonium hexadecyl bromide as precipitant.The crystal structure and microstructure of the products were characterized by XRD?SEM?TEM and XPS to study the effect of the modification of In2O3 nanoparticles on the structure and morphology of the products.The gas sensing performance test results showed that the sensitivity of In2O3/ZnO heterostructure to 100 ppm n-butanol at 370? was 104.3,about 3.5 times and 5.3 times that of ZnO nanorods and In2O3 nanoparticles,and the response-recovery times at 4 ppm were 6 s and 9 s,respectively.By using the theory of BET and band structure,the mechanism of gas sensitivity was clarified.Studies have shown that the presence of In2O3/ZnO heterointerfaces promotes electron transfer and is beneficial to increase the thickness of electron depletion layer and electron stacking layer.In addition,the specific surface area of the In2O3/ZnO heterojunction composite was 39.1 m2/g,and the larger surface area also provides more chemical reaction sites,which can improve the gas sensing performance.The precursor was prepared by hydrothermal method using ZnO powder and SnCl4·5H2O as raw materials and NaOH as precipitant.the Zn2SnO4/ZnO heterojunction composites were prepared by heat treatment of the precursors.the crystal structure and microstructure of the products were characterized by XRD?SEM?TEM and so on.The composition and structure of the materials were investigated for the gas sensing properties of triethylamine,which is a Zn2SnO4/ZnO heterojunction composite.The gas sensing performance test results showed that the sensitivity of Zn2SnO4/ZnO heterostructure to 100 ppm triethylamine at 200? was 175.5,about 30.8 times and 47.4 times that of ZnO nanosheets and Zn2SnO4 nanowire sensors,and the response-recovery times were 10 s and 27 s,respectively.By using the theory of BET and band structure theory were used to further analyze the Zn2SnO4/ZnO heterostructure and elucidated its gas-sensitive mechanism.Studies have shown that The heterointerface of Zn2SnO4/ZnO not only transferd electrons from the conduction band of Zn2SnO4 to ZnO,produced more oxygen negative ions on the ZnO surface,but also promoted electron migration between ZnO nanoparticles,thus improving gas sensitivity. |
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