Study On The Preparation And Gas Sensing Of SnO₂ Nano-material

SnO₂ is a wide bandgap semiconductor gas-sensing material, because its physical and chemical stability, there are many advantages to reducing gas without doping precious metal, such as sensitivity, stability and certain selectivity. The past research mostly focused on the preparation methods or the compositions relation with the gas-sensing properties. This thesis will make systematic study for the relation of preparation methods, morphology and doped with the gas sensing properties.Porous, coral-like and hollow spherical nano-SnO₂ materials were produced by precipitation, hydrothermal synthesis and coating method. The morphology, microstructure and isothermal adsorption-desorption curves were characterized by SEM, XRD and BET. The indirect heating gas sensors were prepared using the three materials. Characteristics of resistance varied with temperature and gas sensitivity of several reducing gases were studied. Results are as follows:(1) The three SnO₂ nano-materials are well crystallized tetragonal system. The porous SnO₂ showing a uniform porous structure, average pore diameter is 8.6nm, the coral-like SnO₂ architecture exhibits a coral-like morphology with many tentacle-like structures, average pore diameter is 13.5nm, the diameter of SnO₂ hollow spherical microspheres are about 1⁴μm, the surface of microspheres is very smooth, but there are holes on its surface, from holes can see that the microspheres are hollow structure with thin walls. The average pore diameter of nanometer grain is 22.7 nm.(2) The prepared materials have higher sensitivities and lower operating temperature. When the operating temperature at 190℃, the sensitivity of the three materials for 100ppm ethanol gas are over 20, as gas concentration increased, the sensitivity and the concentration show a certain linear relationship. Meet the standards for industrial applications.(3) The specific surface area, pore size and pore volume of materials have great influence on gas sensing properties. Under the same conditions, coral-like porous SnO₂ material is more sensitive than porous SnO₂ and hollow spherical SnO₂ materials, and its specific surface area is 40.19m²/g, average pore size is 297.0nm, the pore volume is 0.2984cc/g. But the Ni ion doped SnO₂ porous material under the same conditions is more sensitive than the all three materials. Doping control relative to the structure of the material has a more direct effect on the sensitivity.