Synthesize Of TiO₂/Ag₂V₄O₁₁ Nanoheterostructures And Their Gas-Sensing Applications

With the progress of human industrialization and social modernization,acetone,methane,ethane and other toxic and harmful gases are quietly endangering people’s health,becoming a potential safety hazard.Therefore,it is of great practical significance and commercial application value to design and prepare gas detection elements with high sensitivity,good selectivity,fast response recovery and stable performance.As a typical n-type gas-sensitive semiconductor material,TiO₂ is considered as the most promising gas-sensitive semiconductor material with high chemical stability,good environmental tolerance,non-toxic and harmless,and contact reaction properties.However,due to its small detection upper and lower limits,poor selectivity,long response/recovery time and high working temperature,the industrial application of TiO₂ gas sensor is limited to a certain extent.The transition metal oxide Ag₂V₄O₁₁ has attracted great attention from researchers due to its unique carrier transport channel,fast electronic transport speed and narrow band gap width（2.0 eV）.Moreover,it has become a hot topic to enhance the sensitivity of semiconductor gas sensors by constructing heterogeneous structures.In this paper,nanoparticle TiO₂ and nanowire silver vanadate composite heterogeneous junction materials were synthesized by hydrothermal method,the specific process parameters required in the hydrothermal process were explored,the gas-sensitive properties of composite heterogeneous junction materials were systematically studied,and the mechanism of gas-sensitive enhancement of heterogeneous junction was further explored.The specific research content of this paper includes the following parts:（1）Ag₂V₄O₁₁ nanowires and TiO₂/Ag₂V₄O₁₁ nanoheterostructures materials were prepared by hydrothermal method,the process parameters and the relationship between the parameters and the microstructure were studied systematically,experimental results show that:when the reaction temperature is 180 ^oC,reaction time is 16 h,pH=2.0 can better prepare pure Ag₂V₄O₁₁,and on this basis,a microstructurally controllable heterostructure powder of TiO₂/Ag₂V₄O₁₁ was obtained,the material presented nanowire/nanoparticle structure,and the Ag₂V₄O₁₁ nanowire was about 50 nm in diameter and up to several microns in length.The anatase phase TiO₂ nanoparticles with a diameter of 10 nm were uniformly distributed on the Ag₂V₄O₁₁ nanowire with a diameter of about 30 nm.（2）The gas-sensitive properties of TiO₂/Ag₂V₄O₁₁ nanoheterostructures materials were systematically analyzed,experimental results show that:The heterojunction material samples with TiO2 and Ag2V4O11 molar ratio of 2:1 showed good gas-sensitive response ability to ethanol gas,and the sample with TiO₂/Ag₂V₄O₁₁ molar ratio of 2:1had the best performance.Compared with the pure phase materials,the heterojunction has the advantages of high sensitivity,short response recovery time,good selectivity and low detection lower limit.In particular,the heterojunction can be used for ethanol gas detection at room temperature,where the detection sensitivity of 100 ppm ethanol is 3.6.（3）The gas-sensitive response mechanism of TiO₂/Ag₂V₄O₁₁ nanoheterostructures was studied by means of its electrical properties and energy band structure.The results show that:The carrier concentration of TiO2 is higher than that of Ag2V4O11,while the electron mobility of Ag₂V₄O₁₁ is much higher than that of TiO₂.When Ag₂V₄O₁₁ forms a heterojunction with TiO₂,the electrons on TiO₂ are easily transferred to Ag₂V₄O₁₁,the high electron mobility of Ag₂V₄O₁₁ enables the electrons transferred to it to quickly transfer to the surface and react with the gas,so the gas-sensitive performance is greatly improved.In addition,the formation of heterogeneous junction introduces a lot of interfaces to the material,compared with the pure phase material,the adsorption sites provided by heterogeneous junction are greatly increased,which is of great help to the improvement of gas sensitivity.More importantly,the width of the depletion layer at the heterojunction interface will change significantly with the adsorption/desorption process of the gas,so that the resistivity of the overall material will change more significantly and the gas sensitivity will be greatly improved.