Effect Of Nano-TiO₂ And ZnO On Gas Sensing Properties Of ZnSnO₃

ZnO and SnO₂,wide band gap semiconductors,are the first materials for gas sensing properties study.Their composite metal oxide ZnSnO₃ is a new type of gas sensing material,which has excellent gas sensitivity.So,it has attracted the attention of researchers.However,the operating temperature corresponding to maximum response value of the pure ZnSnO₃ gas sensor is usually above 200oC.Therefore,how to reduce the operating temperature of ZnSnO₃ gas sensor has become the focus and difficulty of experimental research.As the most widely used photocatalytic material,TiO₂ and ZnO have better UV photosensitivity.This research chose TiO₂ and ZnO to modify ZnSnO₃,which reduced the operating temperature of ZnSnO₃ under UV illumination.Firstly,the precursor of ZnSn（OH）₆ was prepared by co-precipitation method,and then was mixed with the modifiers（TiO₂,ZnO,TiO₂-ZnO）.After high temperature annealing,the corresponding composites were obtained.The composite powder was mixed into a pasty state by using water as the binder and applied to the interdigitated electrode sheets.And then,it was dried to obtain a film-type gas sensor.The results show that when the doping concentration of TiO₂ is 10 wt%,nano-TiO₂@ZnSnO₃ shows the maximum gas-sensitivity response（74.21）to 500 ppm ethanol gas and the corresponding operating temperature is 80oC.When the doping concentration of TiO₂ and ZnO is 10 wt%and 0.5wt%,respectively,nano-TiO₂@ZnSnO₃ shows the maximum gas-sensitivity response（75.82）and the corresponding operating temperature is 80oC.It’s suggested in this study that when ZnSnO₃ and TiO₂ are in contact,the heterojunction is formed due to the difference of their band gaps and work functions.A large number of photogenerated electron-hole pairs generated under UV light are separated because of the heterojunction,which accelerates the formation of O-ions and reduces the operating temperature.When TiO₂-ZnO works together,although the absorbance of ZnO on 365 nm ultraviolet light is not as good as that of ZnSnO₃ and TiO₂,the introduction of ZnO allows the accumulated electrons at the interface of ZnSnO₃ and TiO₂ to be fully utilized,which further reduces the operating temperature.In addition,the results compared with previous research show that when the same commercial TiO₂ nanospheres were used to modify ZnSnO₃ with different morphologies,the operating temperature corresponding to maximum response value of the composites was 80oC.Therefore a reasonable explanation was proposed in this research for the above regularity.In summary,ZnSnO₃ hollow cubes is prepared successfully in this paper.And on the basis of this,introducing one or more photocatalytic materials can improve the gas sensitivity of ZnSnO₃ and reduce the operating temperature owing to their excellent optical properties.In general,this study provides a new idea to obtain ZnSnO₃ with uniform morphology and promote the gas sensitivity of ZnSnO₃ with photocatalytic materials.