Controllable Preparation And Modification Of V₂O₅ Nanostructured Materials And Their Properties Studies For Xylene Gas Sensing

As a poisonous gas,xylene poses a great threat to human health.Among the various types of gas sensors,with its advantages of simple structure,small power consumption and low cost,the para-thermal semiconductor gas sensor has attracted wide attention.However,the reported para-thermal xylene gas sensors can not meet the requirements of practical application in operating temperature,response and recovery time.At present,the V₂O₅ thin-film gas sensor has realized the high selection and high response detection of xylene gas at room temperature,so V₂O₅ is considered as a potential material for the development of high-performance xylene gas sensor.In this paper,under the premise of fully considering the production cost,V₂O₅nanoflowers(NFs)and hollow nanospheres(HSs)were synthesized,and the gas-sensitive performance of para-thermal gas sensors constructed by these two nanostructures was studied.Through the Ni²⁺doping of V₂O₅hollow nanospheres,the possible factors for enhancing the gas sensitivity of V₂O₅ HSs to xylene gas after doping with Ni²⁺were studied.Specific research conclusions are as follows:(1)A series of V₂O₅ nanoflowers with different morphologies were prepared by using the simple solvothermal method and heat treatment process by changing the reaction time(0.5,1,2,3 and 4 h),and a para-thermal gas sensor was constructed and its gas sensitivity was studied.The results showed that the V₂O₅ nanoflowers(V₂O₅-3)prepared under the reaction time of 3h showed a hierarchical structure,its size was distributed between 3?5?m,and its specific surface area was 19.5291 m²g^-1.In addition,the gas sensor constructed by V₂O₅-3 samples has the best gas sensitivity performance.Under the optimal working temperature of 300?,its response value to 100 ppm xylene gas is 2.2,and the response/recovery time is 44/78 s,the minimum detection limit is?1 ppm,with good repeatability and long-term stability.The gas-sensitive mechanism between V₂O₅ nanoflowers and xylene gas molecules is attributed to the gas adsorption/desorption phenomenon common in metal oxide semiconductor(MOS)gas sensors.(2)A series of V₂O₅ hollow nanospheres with different sizes were prepared by using the simple solvothermal method and heat treatment process by changing the dosage of VOC₂O₄(5,7,9 and 11 m L),and the corresponding para-thermal gas sensor was constructed and its gas sensitivity was studied.The results showed that the V₂O₅ hollow nanospheres(V₂O₅-7)prepared with VOC₂O₄ content of 7 m L presented a monodisperse morphology with uniform outer diameter,with a size of 500?800 nm and a specific surface area of 5.2333 m²g^-1.Moreover,the gas sensor constructed by V₂O₅-7 sample has the best gas sensitivity performance.Under the optimal operating temperature of 290?,its response value to 100 ppm xylene gas is 2.75,the response/recovery time is 21/134 s,the minimum detection limit is?1 ppm,and it has good repeatability and long-term stability.(3)Using the simple solvothermal method and heat treatment process,the V₂O₅-7precursor(VO₂-7)prepared in(2)was doped with Ni²⁺(Ni²⁺doped at concentrations of 1.15,2.97 and 5.10 at%,respectively)by changing the dosage of Ni(NO₃)₂·6H₂O(0.08,0.24 and0.36 g),and a para-thermal gas sensor was constructed with the doped product and its gas sensitivity was studied.The results showed that the optimal operating temperature of the V₂O₅gas sensor after Ni²⁺doping decreased from 290?to 265?,and the selectivity of the sensor to xylene gas remained unchanged.Among them,the gas sensor constructed by the V₂O₅ hollow nanospheres(Ni²⁺doped at 2.97 at%)(Ni@V₂O₅ HSs-2)has the best gas sensitivity.Its response value to 100 ppm xylene gas at 265?is 5.2,and the response/recovery time is 16/384s.In addition,the minimum detection concentration of all sensors for xylene gas is?500 ppb,and has good repeatability and long-term stability.The factors to enhance the gas-sensitive performance of Ni²⁺doped V₂O₅ HSs on xylene gas were as follows:the specific surface area of V₂O₅HSs after Ni²⁺doping increased,and the oxygen content of surface defects increased.The specific surface area of Ni@V₂O₅ HSs-2(50.6493 m²g^-1)was?10 times that of V₂O₅ HSs,and the surface defect oxygen content(49.23%)was?1.7 times that of V₂O₅HSs.