The Preparation And Gas-sensing Properties Of Vanadium Dioxide/Zinc Oxide Hierarchical Hetero-structure

With the development of the modern economy,the industrialization in our country has improved continuously.The environmental problems closely related to the survival and development of mankind are also becoming increasingly prominent.Nowadays,the demand for high-performance gas sensors,which can effectively monitor the content of flammable,explosive,poisonous gases and air pollutants in real time,is more urgent in our society.There are various gas sensors,among them metal oxide semiconductor gas sensors have been widely studied and used,because of their high sensitivity,simple device structure and low production cost.The metal oxide semiconductor zinc oxide（ZnO）is one kind of the traditional mainstream gas-sensing materials.The ZnO-based nanostructure sensors have achieved the rapid and effective detection of poisonous and noxious gases,such as ethanol,acetone and ammonia gas.However,such sensors generally need working on high temperature and have high power consumption,which limits their application in many fields.Due to the unique metal-insulator transition property,vanadium dioxide（VO₂）drew widespread attention.In recent years,the research has found that VO₂ has great potential for detecting toxic and harmful gases at room temperature.But the sensitivity of VO₂-based gas sensors has yet to be improved.Based on the above situation,this paper proposes a VO₂/ZnO hierarchical hetero-structure,aiming to achieve effective detection of toxic and harmful gases at room temperature by combining the advantages of these two materials.In this paper,we mainly study from three aspects:Firstly,the influence of experimental parameters of the hydrothermal process on the morphology of VO₂nanostructures was studied,and the corresponding room-temperature gas-sensing performances of pure VO₂ nanostructure sensor under the optimal experimental parameters were studied.Next,the effect of ZnO growth time and the concentration of ZnO growth solution in the phase composition,micro-morphology and gas-sensing properties of VO₂/ZnO hierarchical hetero-structure was investigated.And we also discussed the corresponding gas-sensing mechanism of the composite structure sensor.The structure,component and surface morphology of the samples were characterized by XRD,SEM and TEM.The gas-sensing tests of the as prepared gas sensors were carried out on the gas-sensitive testing platform of our laboratory.As the results show,when the concentration of oxalic acid and vanadium pentoxide precursor is 0.075mol/L and 0.025mol/L respectively,and their mole ratio is 3:1,meantime the hydrothermal time is 36h and the hydrothermal temperature is 180℃,B-phase VO₂ nanorods with homogeneous morphology and no other composition can be prepared.Pure VO₂ sensor exhibits the performances of p-type semiconductor at room temperature.It has gas response to the four tested gases（acetone,ethanol,ammonia,nitrogen dioxide）,but the gas response is low.The prepared VO₂/ZnO hierarchical hetero-structure shows branch-like morphology,and the sensor with ZnO growth time of 4h has the highest gas response to acetone at room temperature.When the gas concentration is 100ppm,the response value is 4.51,the corresponding response time and recovery time is 8s and 18s respectively.Besides,when the concentration of ZnO growth solution is 0.01mol/L,the corresponding composite structure sensor shows outstanding selectivity to ammonia at room temperature and the response time is short（2-5s）.