Synthesis And Gas-sensitive Properties Research Of Graphene-like MoS₂ Thin Films

The rapid development of economy demands more and more energy.Excessive energy consumption has seriously damaged the human ecological environment and caused environmental pollution.In particular,a large amount of industrial waste gas is discharged untreated.These are serious threats to human life.As an important tool for identifying gas types and detecting gas concentration in real time,gas-sensitive sensor has gradually become the focus of research.Typical semiconductor oxide sensors such as Sn O₂,Ti O₂and ZnO can realize the function of detecting target gas.However,the development of these sensors is limited by their fatal shortcomings,such as poor selectivity,high test operating temperature,high power consumption and short service life.In this paper,the gas-sensitive properties of monolayer,bilayer and trilayer MoS₂and MoS₂composite structures are studied by theoretical calculation and experimental preparation.A ppb grade gas sensor with low detection limit and high sensitivity was produced.The main research contents and results of this paper are as follows:First,first-principles calculation were used to simulate the adsorption properties of NO gas molecules on monolayer,bilayer and trilayer MoS₂.The typical adsorption point location,band structure,partial density of states and gas sensitive mechanism of MoS₂were studied.The calculated results show that different layers of MoS₂are the best adsorption sites for NO molecules.The adsorption of NO on bilayer MoS₂is preferred and the adsorption on monolayer MoS₂is considered next.With the increase of MoS₂layer,the number of NO adsorbable sites decreases gradually.Therefore,bilayer MoS₂is the best material to adsorb NO gas molecules from the perspective of the number of layers.For interlayer adsorption,NO gas molecules are more inclined to adsorb to the surface of MoS₂.The increase of the number of MoS₂layers increases the possibility of NO adsorption between the layers.Secondly,the hydrothermal method is used to prepare the MoS₂nanomaterials.The growth mechanism of flake MoS₂nanomaterials was analyzed and explained.The results show that serious agglomeration occurs when MoS₂nanomaterials are prepared by conventional hydrothermal method.The process is optimized to introduce reaction additives which can effectively improve the dispersion state of flake MoS₂nanomaterials.Thinner and more uniform MoS₂nanomaterials have been successfully produced.The finished nanomaterials were tested for their gas-sensitive properties.The results show that the flake MoS₂nanomaterials have good selectivity to NO₂gas.When the working temperature is 300?,the detection limit of NO₂gas is 100 ppb and the detection range is100 ppb?10 ppm.When the concentration of NO₂gas is 10 ppm,the responsiveness reaches 38.3,the response time is 10 s,and the recovery time is 18 s.Thirdly,the hydrothermal process is used to make MoS₂@ZnO nanocomposites.The orthogonal experimental method was used to optimize the process parameters.MoS₂@ZnO heterojunction nanocomposites with excellent gas sensitivity were fabricated.It is used for characterization analysis and gas sensitivity testing of materials using NO₂gas.The results show that the optimum technological parameters for hydrothermal preparation of MoS₂@ZnO nanocomposites are as follows.The p H of hydrothermal solution is 6.0.The hydrothermal reaction time t=10 h.Molybdenum/sulfur ratio[Mo]/[S]=1/4.The hydrothermal reaction temperature T=190?.The MoS₂@ZnO nanocomposite was prepared with good crystalline quality and uniform structure of MoS₂nanosheets.The MoS₂@ZnO nanocomposite was successfully used to fabricate a micro gas sensor.When the concentration of NO₂gas is 1 ppm,the responsiveness is 25.5,the response time is 7 s and the recovery time is 18 s.It has good stability.Finally,low pressure CVD technology was successfully used to fabricate a monolayer MoS₂nanofilms.The orthogonal experimental method is used to influence the CVD process parameters of MoS₂film thickness.It was optimized to get the new process parameters as follows.Distance between sulfur source and molybdenum source=25 cm.Carrier flow=60 sccm.Reaction temperature T=780?.Reaction time t=5 min.The heating rate was 10?/min.As a template for MoS₂growth,PTCDA was successfully used to fabricate a monolayer MoS₂nanofilm with a transverse size of nearly 90?m.The test results show that the monolayer MoS₂film has a good performance in detecting the micro concentration of NO₂gas.