Study Of The Fabrication And Properties Of PbS@MS₂（M=Mo,W）Gas Sensors

With the rapid development of industrial science and technology,gas sensors have been widely used in the field of artificial intelligence,industrial and agricultural production,environmental monitoring and medical treatment,etc.So,it is of great significance to explore a kind of gas sensor with high performance,high precision,high reliability,low power consumption and low cost.In this work,MoS2,PbS@MoS2 and PbS@WS2 are synthesized by hydrothermal method combining with chemical precipitation,and the crystal structure,microstructure,material composition and surface chemical state of them are characterized.All of these materials are fabricated into the gas sensor to investigate their gas sensing properties and sensing mechanism.The main research contents are as follows:1.The MoS₂ nano-flower was prepared by hydrothermal synthesis,and MoS₂ is fabricated into the gas sensors to investigate their gas sensing properties.It can be found that the pure MoS₂ gas sensor exhibits different response behaviors with increase of NO₂ concentrations.At low NO₂ concentrations（5-50 ppm）,the MoS₂ gas sensor shows a negative response（n-type）,while it exhibits positive response（p-type）at high NO₂ concentrations（100-400 ppm）.There are two possible reasons for the n-p transition:NO₂ and O₂ capture electrons from the MoS₂ surface so that the electron concentration decreases,thus affecting the carrier type of MoS₂.Moreover,the MoS₂gas sensor shows a fast response/recovery rate at room temperature,but with difficult desorption,low response and bad stability.It is ascribed to the fact that MoS₂ is easily oxidized in air,which reduce the performance of the MoS₂ gas sensor and it is difficult to achieve our expected performance.2.A novel composite of PbS quantum dots-modified MoS₂（PbS@MoS₂）is synthesized by hydrothermal method combining with chemical precipitation,and fabricated into the gas sensor to investigate its enhanced gas sensing properties caused by the modification of PbS quantum dots at room temperature.It is found that the responsivity of PbS@MoS2 is obviously higher than that of pure MoS2 gas sensor throughout the whole test range,and PbS@MoS₂ gas sensor is of better selectivity compared with pure MoS₂ gas sensor at room temperature.The response of PbS@MoS₂ gas sensor is about 50 times higher than that of MoS₂ gas sensor at 100ppm NO₂ concentration.The recovery behavior is greatly improved,and the resistance of MoS₂/PbS gas sensor can return completely with almost no drift（The recovery ratio is more than 99%）.The enhanced gas sensing properties of PbS@MoS2,which are superior to that of pure MoS2,are ascribe to the large surface area of MoS2combine with the high responsivity of PbS QDs for NO2,and the formation of heterojunctions leads to the competitive adsorption of the target gases,which can prevent MoS2 from being oxidized,further improving the stability of gas sensor.Furthermore,in order to profoundly discuss the enhanced performances and the sensing mechanism,the molecular models of adsorption systems are constructed to calculate the adsorption energies and the diffusion characters of NO2 via density functional theory.3.We have successfully synthesized the PbS@WS₂ composite by chemical precipitation,and the gas sensing properties of WS₂ and PbS@WS₂ at the whole test range are compared to investigate the enhanced performance caused by the modification of PbS QDs.The results show that the responsivity of PbS@WS₂ gas sensor is obviously enhanced compared with pure WS₂ gas sensor throughout the whole test range,and the resistance of PbS@WS2 gas sensor can fully recover to the original value at room temperature,indicating the modification of PbS QDs can effectively enhance the responsivity and recovery behavior to NO2 gas of pure WS2gas sensor.When the proportion of PbS in compesite exceeds a certain amount,the response type of the PbS@WS₂ composite are consistent with PbS.The enhanced gas sensing properties of PbS@WS₂ gas sensor may indicate that the modification of PbS quantum dots can regularly improve the gas sensitivity of TMDs materials at room temperature,especially the stability and recovery characteristics of TMDs materials.