Research On The Controllable Preparation And Gas Sensitivity Of MoS₂-based Composites

Nitrogen oxides?NO_x?are one of the main gaseous pollutants in the atmosphere.It is one of majors air pollutions for acid rain and photochemical smog,which causes serious disease to humans.For example,NO_x is easy to combine with human hemoglobin in the blood,and also stimulate the lung,causing a lot of serious diseases.Therefore,enormous number of gas sensors with different detection mechanisms have been explored to monitoring NO_x concentration.Foremost among these are the semiconductor oxides sensors.To some extent,these gas sensors could detect NO_x well.But they require a high working temperature and have low sensitivity,poor selectivity at room temperature?RT?.Hence,it is necessary to develop NO_x gas semiconductor oxides sensor with high sensitivity,fast response,good selectivity and stability,and recovery time and which could be used better at RT.MoS₂,a p-type semiconductor,is a promising layered material which is similar to graphene in electrical conductivity and mechanical strength,receiving increasing attention due to it overcomes the disadvantages of graphene?such as zero band gap?and possesses its advantages.In this paper,a series of molybdenum disulfide composites prepared by hydrothermal method are studied systematically.The properties of the molybdenum disulfide-based composites are improved by adjusting the reaction temperature,different concentrations and reaction time.The main contents are as following:Firstly,a series of molybdenum disulfide nanoflowers were prepared by simple hydrothermal method by adjusting reaction time and temperature,and their gas sensitivity to nitrogen oxides was studied.The results showed that pure molybdenum disulfide was the best property and morphology when the reaction temperature was200?and the reaction time was 24 h,which provided a good foundation for the subsequent research on the molybdenum disulfide composites.Secondly,p-type Mg?OH?₂/MoS₂ composites were fabricated by hydrothermal method using pure molybdenum disulfide as precursor.Mg?OH?₂ serve as alkaline center,can promote acid gas NO_x in the adsorption and chemical reaction between the gas and the material surface,accelerating the speed of adsorption and reaction,greatly reduce the time response.In addition,sodium dodecyl sulfate?SDS?was used as an intercalation and template in order to increase the specific surface area.The 2-Mg-MoS₂sensor detects NO_x in the air at room temperature with excellent stable sensing performance,excellent reversibility,selectivity and high response:100ppm nitrogen oxide the response is 4.73 at 25%relative humidity and room temperature,the response time is only 3s.Finally,Ag/MoS₂ flower balls with different molar ratios were prepared via doped silver nanoparticles with pure MoS₂ by simple water bath method.The samples are characterized by XRD,BET and SEM techniques.The analysis results shown that the introduction of Ag nanoparticles greatly enhances the response due to chemical and electronic sensitization.Electron sensitization is the direct exchange of electrons between semiconductors and precious metal particles.The synthesized Ag/MoS₂composite materials presents excellent sensing performance to NO_x gas at room temperature with the highest response?5.19 to 100 ppm?,fast response time?2 s to 100ppm?.