Preparation And Gas-sensitive Properties Of Tin Dioxide Nanomaterials

The demand for air quality in the living environment and industrial production has been increasing in recent years.The development of sensors has not only achieved effective detection of air quality in the environment,but also effectively prevented some dangerous situations from occurring.Among numerous sensors,metal oxide semiconductor gas sensors have become a topic of interest in the field of gas sensors due to their high level of sensitivity and fast response-recovery speed.However,the recognition conversion function of metal oxide semiconductor gas sensors and the utilizing effectiveness of sensitized materials are still constrained by the microstructure and morphology of materials.The integration of the nanotechnology and semiconductor gas sensing technology has effectively improved the surface activity of the sensing material and the utilization of the material,which has provided a great opportunity for the production of high-performance gas sensors.The preparation of gas sensing materials with high specific surface area,high air attack rate,surface permeability and good permeability is an effective way to improve the gas-sensitive performance of materials.In this thesis,we designed and prepared tin dioxide based gas-sensitive materials with different morphological structures from the material structure design,and used its structural advantages to achieve"structural sensing".Using the principle of interaction between different materials,a second component with catalytic activity was modified on the surface of Sn O₂to construct heterogeneous contacts at the micro and nano scale to further improve the gas-sensitive properties of the material and realize the"modified sensitization"of the material.The main research of the paper is as follows.1.Monolayer hollow tin dioxide nanospheres with hollow structure were prepared by hydrothermal method using carbon spheres as a template assisted by high-temperature calcination,and plain morphology tin dioxide particles were prepared as a control.The gas-sensitive properties of tin dioxide nanoparticles and hollow tin dioxide nanospheres were investigated in detail using ethanol as the target gas.The reasons for the enhancement of the gas-sensitive properties by the hollow structure were discussed in terms of the morphological structure of the materials by SEM and TEM.2.Tin dioxide monolayer nanospheres with different contents of silver doping（from 0at%to 15 at%）in hollow structure were prepared by hydrothermal method combined with high temperature calcination using carbon spheres as templates.The morphology,microstructure and composition of the hollow nanospheres were characterized by other characterization methods such as XRD,SEM and TEM.The results demonstrate that the prepared ones are spherical shell structures formed by the combination of monolayer nanoparticles,and a large number of mesoporous structures are formed on the surface.The doped samples contain both Sn,O,Ag,and C elements.The gas sensitive performance of the fabricated materials was tested,and the result showed that the doping not only reduced the working temperature of the materials（240°C for pure and 180°C for silver-doped）,but also increased the response value of the materials,which was more than 10 times higher than that of the pure gas-sensitive materials at the same ethanol concentration.In addition,the response and response time and stability of the 8 at%silver-doped tin dioxide material were tested.The results demonstrate that the doping can effectively improve the gas-sensitive performance of the material.3.Pure Sn O₂nano-flowers and Ce-Sn O₂nano-flowers with Ce content of 1 at%,3 at%and 5 at%were prepared successfully by hydrothermal calcination assisted by CTAB as catalyst.The morphologies and crystalline structure of the prepared sample were studied by means of energy dispersive x-ray spectroscopy,scanning electronic microscopy and transmittance electron microscopy.The gas sensing behaviors of the fabricated sensors were systematically investigated.The proposed process showed that Ce doping obviously decreased the optimum operating temperature and greatly increased the sensing capability of the Sn O₂-based gas sensor.The sample doped with 5 at%Ce exhibited ultra-sensitivity,excellent selectivity,long-time stability and quick response/recovery time of 7 s/9 s to 200ppm ethanol at the optimum operating temperature of 125℃.Furthermore,the gas sensing mechanism was also discussed in detail.