Gas Sensitive Properties Of Oxide Semiconductor Host-guest Composite

Gas sensing technology has been developed rapidly in recent years,more and more gas sensing materials are being discovered.Among them,the semiconductor metal oxide gas sensors have the advantages of the higher sensitivity,the lower cost,the faster respond-recovery,the more excellent long-term stability and selectivity.Therefore,semiconductor metal oxides have become the main materials for preparing gas sensors.In this thesis,the host-guest gas sensitive materials based on ZnO and SnO₂ were prepared by template method and hydrothermal method,the related comprehensive gas sensing performance of the prepared materials were studied.The specific research contents are as follows:A kind of monodisperse ordered mesoporous In₂O₃/ZnO host-guest composite with novel sedum lineare flower like morphology was prepared by template following with calcination method.The diameter of the flower-like structure particles of the material was about 1.7?m,the flower-like structure were self-assembled by nanosheets with 118 nm thickness,and the ordered mesoporous were distributed on the surface of the petals whose diameter was about 33.49 nm.This unique flower-like porous structure contributed the material with the larger specific surface area which reached to 93.644 m²g^-1.Under room temperature,the flower-like In₂O₃/ZnO gas-sensitive composite showed the excellent gas-sensitive response to H₂S gas,whose response to 100 ppm hydrogen sulfide gas reached to 10.2,which was about 8.5 times of the response of pure ZnO matrix.The detection limit of the material for hydrogen sulfide gas was as low as 1 ppm,and it also showed the excellent selectivity towards hydrogen sulfide gas.The porous ZnO/SnO₂ host-guest composite with regular octahedral structure was prepared by hydrothermal method,and the size of the octahedron particles was about 2-4?m.The influence of the hydrothermal time on the morphology and gas-sensitive properties of the prepared material was investigated by keeping the hydrothermal temperature at150°C.When the hydrothermal time was 16 h,the prepared ZnO/SnO₂ gas-sensitive material had the largest specific surface area,which reached to 90.913 m²g^-1.This material showed the excellent gas-sensitive response towards ethanol gas at 200°C.When the concentration of ethanol gas was 100 ppm,the response of the gas sensor based on this material reached to 17.8.The response of the gas sensor to 1 ppm ethanol gas could still reach to 2.35,and the corresponding response time was only 2.3 s.The prepared material had excellent selectivity towards ethanol gas.The porous ZnO microsphere with tumbleweed-like structure was prepared by hydrothermal following with calcination method.The diameter of the microsphere was about 8±2?m,and the specific surface area could reach to 94.137 m²g^-1.Through a series of comparative experiments,the optimal synthesis conditions of the ZnO microsphere were determined.The morphology and the gas sensitive property to nitrogen oxide gas of the prepared ZnO microsphere were analyzed and tested.The results showed that the response of the gas sensor based on this material to 100 ppm nitrogen oxide gas could reach to 80.3at 180°C.The detection limit was as low as 0.5 ppm.It also had the excellent gas selectivity and long-term stability to nitrogen oxides gas.