Study On Construction Of Porous SiO₂ Or ZnO Based Composites And Their Gas Sensitive Properties

Nitrogen oxide（NO_x）is one of the most toxic air pollutants,which can cause environmental problems and respiratory tract infections.When people are exposed to high concentrations of nitrogen oxides for a long time,NO_x can irritate their throats and lungs,and even develop cancer.In this paper,SiO2 or ZnO matrix composites were prepared by chemical deposition,electro-deposition and hydrothermal method,and their gas sensing properties were investigated.The specific summary was as follows:In this thesis,the ordered mesoporous WO₃/SBA-15 composite material was prepared by ultrasonic chemical deposition method and the obtained amorphous composite material demonstrated semiconductor properties.The effect of different ultrasonic chemical deposition time on gas sensitivity was investigated.This composite material maintained the original fibre morphology and ordered mesoporous structure of SBA-15 molecular sieve.When the ultrasonic chemical deposition time was 2 h,the composite showed the highest response.At room temperature,the response to 100 ppm NO_x gas reached up to 96.6%,and the response time was only 5 s.The detection limit was only 1 ppm,and it had much better selectivity to NOx gas.The porous CuO/ZnO composite was prepared by the combination of chemical deposition method with electro-deposition method.When the electro-deposition time was kept at 1 h,the effect of electro-deposition current on gas sensitivity was investigated.When the electro-deposition current was 1 A,the composite had the highest sensitivity and selectivity.At room temperature,the response of the material to 100 ppm NO_x gas reached up to 91.5%,the response time was 11.5 s,the detection limit was only 0.5 ppm,and it showed much better selectivity to NOx gas.The ordered porous ZnO based material was prepared by soft template method,and then different proportions of Sn²⁺were doped into the ZnO material by using hydrothermal method via sodium sulfosalicylate,and further the composite was calcined at high temperature to obtain SnO2/ZnO composite.The material had a novel multi-cube morphology.When the doping ratio of SnO₂ was 30 wt%,the composite had the highest response.At room temperature,the response to 100 ppm NO_x gas was 60.5%,the response time was only 2 s,the detection limit was only 0.2 ppm,and it exhibited much better selectivity to NOx gas.The ordered porous ZnO based material prepared by soft template method.The porous NiO/ZnO composite was prepared by the combination of chemical deposition and electro-deposition method.The electro-deposition current was kept at 1 A,the influence of different electrodeposition times on the gas sensing performance was studied.When the electro-deposition time was first at 45 min,the response of the composite to 100 ppm NO_x reached 74.0%,response time and detection limit was respectively 21 s and 1 ppm,and it displayed much better selectivity to NO_x gas.