| The rapid development of industrialization has brought human rich at the same time also produced a large amount of waste material,caused the serious environmental pollution,especially large amounts of VOCs gases emission the atmospheric environmental degradation caused by the human production and life constitutes the great threat.Therefore,accurate real-time monitoring of VOCs in the production and living environment is vital to ensure the safety of production and quality of life.Semiconductor oxide gas sensor has the advantages of low cost,sensitive response and high stability,and has been widely used in gas monitoring field.Metal oxide semiconductor as this kind of sensor is sensitive to the core of the material,its composition and structure directly determines the performance of gas sensor,so the micro mesoscopic composition and structure of the semiconductor oxide regulation to build high-performance gas sensitive materials,to promote the development of high performance semiconductor oxide gas sensor has the vital significance.As gas sensitive research gradually thorough,the study found that the specific surface area,particle size,hole structure,surface composition and structure on the response of the material value,response speed,selectivity and stability performance has an important influence;Therefore,people usually adopted to optimize the mesoscopic structure built,precious metals,doping modification,heterogeneous structure modification methods on the material of the specific surface area,particle size,hole structure,regulation and control of surface composition and structure,to enhance the gas-sensing properties of materials.Layered metal hydroxides(LDHs)is a kind of important layered inorganic functional materials,the metal ions on the layer board were atomic highly fragmented and has the nature of the composition and structure are greatly modulation.Based on these important properties of LDHs,this paper carried out the layered structure of precursor method to construct multilevel metal oxide gas sensitive materials,first using hydrothermal prepared by two-dimensional layered hydroxide nanometer assembly of multistage structure,through roasting the precursor topology into multi-level structure of metal oxide sensitive materials,and its composition,structure and properties were characterized and test analysis,the specific research results are as follows:1.A Co-doped Zn(OH)2 hierarchical structure layered precursor with Co/Zn molar ratios of 1%,3%,5%and 10 at.%was prepared by a hydrothermal method and calcined at 300 °C to obtain the Co doped ZnO hierarchical structure is constructed by thin sheets with nanoparticles.The Co doped ZnO hierarchical structure has a smaller nanoparticle size,a higher specific surface area(110 m2/g)and a rich mesoporous structure.The Co doped ZnO structures were characterized by HRTEM,XRD,BET,XPS and Hall effects.It was proved that Co doping not only increased the specific surface area of ZnO hierarchical structure,but also improved the material carrier concentration and surface active oxygen species content.The gas sensitivity test results shows that the hierarchical structure ZnO with 5 at.%Co doping has the best gas sensitivity to ethanol gas.The response to 50 ppm ethanol at 150 °C operating temperature is as high as 54.5,which is higher than that of ZnO and the response value is increased by 6 times,the optimal operating temperature is reduced by 20 °C,the response and recovery times are 36 s and 21 s,respectively,and the detection limit is as low as 45.4 ppb.At the same time,it exhibits excellent selectivity,high stability,and wide linear range.2.CoSn-LDH precursors with Co/Sn molar ratios of 3,6,9 and 20 were prepared by homogeneous precipitation method.The hierarchical structure Co3O4/SnO2 composites were prepared by calcining the CoSn-LDH precursors at 350 °C.The results of XRD characterization showed that Co3O4-SnO2 composite oxides were formed after calcination of the precursors,and the samples with a Co/Sn molar ratio of 9 were further analyzed by HRTEM.It was found that Co3O4 and SnO2 nanoparticles formed p-n heterojunctions.Through the gas sensitivity test,it was found that the p-n heterojunction constructed by introducing SnO2 into Co3O4 can significantly improve the gas-sensing performance.Among them,the sample with the Co/Sn molar ratio of 9 exhibits the best gas-sensitivity to acetone gas.The response to 50 ppm acetone at operating temperature(90 °C)reached 52,and the response-recovery time was 161s and 92 s,respectively.Compared to the pure Co3O4 and SnO2 components,the response of the Co3O4-SnO2 increased by 3.7 and 4.9 times,and the optimal operating temperature decreased by 40 and 80 °C,respectively.3.A hierarchical structure CoIn-LDH precursor with Co/In molar ratios of 2,3,4,6 and 9 was prepared by hydrothermal method.A series of clustered Co3O4/In2O3 p-n heterojunctions were constructed by calcining at 350 °C.XRD,SEM,HRTEM and BET were used to characterize the crystal structure,microstructure and pore structure of hierarchical structure Co3O4/In2O3 p-n heterojunction.It was found that both Co3O4 and In2O3 crystal phases exist in the Co3O4/In2O3 composite,the specific surface area of 85 m2/g and abundant mesopores with a size of 3-15 nm.The Raman and XPS were used to study the surface structure of hierarchical structure Co3O4/In2O3 p-n heterojunctions.It was found that Co3O4/In2O3 p-n heterojunction materials had more defect sites and surface active oxygen species.The gas sensitivity test results shows that the hierarchical structure Co3O4/In2O3 p-n heterojunction has excellent gas-sensitivity at low temperature,in which the Co/In molar ratio of 3 Co3O4/In2O3 heterojunction at 80 ? to 50 ppm acetone reaching 153,it is 14.7 and 15.4 times that of pure Co3O4 and In2O3,and the best operating temperature is reduced by 50 and 70 °C,respectively.In addition,the heterojunction exhibits excellent selectivity to the acetone gas,good repeatability,and excellent Stability,after 30 days of testing,the response was only reduced by 6.1%. |
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