Preparation And VOCs Sensing Properties Of Perovskite-type ZnSnO₃ Nanocubes

Organic solvents acted as main source materials are widely used in industrial production process,which are usually flammable and explosive,and are easily volitilized into harmful gases of VOCs to human being.Therefore,high-performance gas sensor for VOCs gas detection is of great siginificance to human life and wealth security.Gas sensors based on metal oxide semiconductors have been widely used in practical application due to their excellent advantages,such as high sensitivity,fast response/recovery speed,and easy to carry.However,the development of such gas sensing materials is mainly focused on binary metal oxide semiconductors,while ternary metal oxide semiconductors with unique structures are rarely investigated.ZnSnO3 is a typical n-type ternary metal oxide semiconductor material with perovskite structure,which is widely used in photocatalyst,piezoelectric device and solar cell yields because of its large electron mobility,high catalytic activity,and abundant active sites,etc.Noble metal doping is an effective route to improve gas sensing prerformance of the sensing materials.However,the effects of the type of noble metal doping element on sensing properties of the sensing materials are rarely considered.In this thesis,the perovskite-type ZnSnO3 nanocubes were optimally synthesized by a hydrothermal method,and the influence of the type of noble metal doping element on their morphology and gas sensing properties were investigated.In this work,ZnSnO3 nanomaterials were prepared by a hydrothermal method,where zinc sulfate and tin chloride were used as the zinc source and tin source,respectively,and hexa methyltetramine was used as the sufactants.The microstructure and surface morphology of ZnSnO3 nanomaterials were characterized by XRD and SEM.By optimizing the preparation conditions in hydrothermal process,the optimal preparation conditions were determined as follows,namely,precursor pH value of 11,reaction temperature of 140℃,and reaction time of 8 h.At such optimal preparation conditions,the obtained ZnSnO3 nanomaterials showed superior structural properties such as small size,regular morphology,and uniform dispersion.Noble metal(Pt,Au and Ag)solution was dropped into the precursor solution to synthesize noble metal doped-ZnSnO3 nanocubes.The microstructures of undoped and noble metal dopedZnSnO3 nanocubes were characterized by XRD,SEM,TEM and XPS.It shows that the noble metal doped-ZnSnO3 nanomaterials still have the morphology of nanocubes with perovskite structure,and the noble metal elements are uniformly dispersed on the surface of ZnSnO3 nanocubes.With the increase of noble metal element concentration,the size of ZnSnO3 nanocubes slightly decreases.Gas sensors were fabricated by dispersing the corresponding ZnSnO3 nanocubes on the ceramic electrodes to investigate the ethanol sensing properties via a static gas sensing test system.It demonstrates that ZnSnO3 nanocubes with noble metal doping show more excellent sensing properties compared with undoped ZnSnO3 nanocubes.Noble metal doping not only effectively enhances the sensor response,but also obviously improves the ethanol selectivity of the sensing materials.At the same noble metal element concentrate and testing conditions,the order of the enhancement effect of gas sensing properties of the obtained products is Ag doping>Au doping>Pt doping.The theory of electron depletion layer is used to clarify the variation trend of carrier concentration and mobility of ZnSnO3 nanoubes during gas adsorption process.In the aspect of improving gas sensing property by noble metal doping,the enhancement can be explained by electron sensitization,chemical sensitization and work function difference of the sensing materials.The effect of different noble metals doping element on the occurrence of gas sensing reaction is analyzed,and the gas sensing reaction mechanism of perovskite-type ZnSnO3 nanoubes with different noble metal doping elements to ethanol gas was clarified.This work provides a new route to synthesize perovskite-type ZnSnO3 nanomaterials,also proves that effective selection of noble metal doping element may significantly improve its sensing property.It is helpful to expand the practical application potential of ZnSnO3 nanomaterials in gas sensor field.