Structural Modification Of Transition Metal Sulfides And Mechanism Of Enhanced Gas Sensing Properties

Gas sensors play an important role in the industry,medical treatment,military and daily life.Among them,the semiconductor gas sensor has become one of the most widely used gas detection equipment due to its advantages of fast response,high sensitivity,low cost,etc.MoSe₂is one of the typical transition metal dichalcogenides(TMCDs)with a graphene-like layered structure,large specific surface area and adjustable bandgap,which have great application potential in the field of the gas sensor.In this paper,1T/2H-MoSe₂nanosheets were prepared by the hydrothermal method.The influence of microstructure and phase on the gas sensitivity of MoSe₂nanosheets was studied.To improve the gas-sensitive performance of1T/2H-MoSe₂nanosheets,the gas sensors based on Au@1T/2H-MoSe₂and Cu@1T/2H-MoSe₂nanosheets were prepared utilizing metal particle modification,and the gas sensitivity test was carried out.The mechanism of the effect of phase and modification on gas sensitivity was analyzed by First-Principles Calculation.The main research contents and results are as follows:(1)MoSe₂nanosheets with different micromorphology and phase were prepared by adjusting the reaction temperature and reaction time of the hydrothermal method.At the same reaction temperature,MoSe₂nanosheets gradually grow up from small size clusters,and then aggregate into nano-particles with the increase of reaction time.Meanwhile,part of the 2H phase MoSe₂phase will change into 1T phase in the reaction process,forming 1T/2H phase heterostructure,which improves the electrical transport capacity of the material.Under the conditions of reaction temperature of 200?and reaction time of 16 hours,the prepared MoSe₂nanosheets shows good gas-sensitive properties to NO₂gas.If the reaction time is shortened,the crystallinity of MoSe₂nanosheets is low.If the reaction time is prolonged,MoSe₂aggregates into granules,which reduces the active sites for gas adsorption.Compared with NH₃,H₂S and SO₂,1T/2H-MoSe₂nanosheets has higher adsorption energy and stronger charge transfer capacity for NO₂gas adsorption showed by the result of the First-Principles Calculation.In conclusion,under the optimal reaction conditions,the content of 1T phase in prepared MoSe₂is higher,which has good electrical conductivity.More gas adsorption sites can be provided by the exposed edge of the nanosheets structure.(2)Au@1T/2H-MoSe₂and Cu@1T/2H-MoSe₂nanomaterials were prepared by the means of metal nanoparticles with high conductivity decoration on the surface of1T/2H-MoSe₂nanosheets,to improve the gas sensitivity of NO₂gas.For the Au@1T/2H-MoSe₂nanosheets,the size of Au particles is about 10 nm,attached to the surface of 1T/2H-MoSe₂lamella.The response to NO₂is increased by 23.1%,and has a faster response time.For Cu@1T/2H-MoSe₂nanosheets,the size of Cu particles is about 30-50 nm,showing the phenomenon of metal particles aggregation.The sensitivity of the sensor based on Cu@1T/2H-MoSe₂to NO₂gas is improved by 41.7%,and the sensor has excellent dynamic response-recovery characteristics.First-Principles Calculation shows that the adsorption energy of Cu@1T/2H-MoSe₂crystal structure for NO₂is higher than that of Au@1T/2H-MoSe₂and 1T/2H-MoSe₂crystal structure.And the charge transfer capacity is also enhanced,which is beneficial to the gas-sensitive reaction.Metal nanoparticles can be used as catalysts for the reaction between gas and material,which can improve the charge transfer rate between gas and material and improve the gas-sensitive response performance.The modification of Cu particles alleviates the stacking of 1T/2H-MoSe₂nanami clusters,exposes more active edges,and shows a more excellent gas-sensitive response to NO₂.