Controllable Preparation Of Composite Materials Based On Few-layers MoS₂ And Their Room Temperature NO₂ Gas Sensitivity

As industrial production safety,environmental pollution and other issues have attracted much attention,there is an urgent need to effectively detect indoor and outdoor environmental pollutants.Therefore,we have put forward higher requirements for the performance of the sensor.In recent years,MoS₂ has become a unique and highly potential sensing material due to its adjustable morphology and lamella structure,as well as changes in electrical and chemical properties with the number of layers.However,as a room temperature gas sensing material,its low detection sensitivity,long recovery time and incomplete recovery are the main problems currently faced.Therefore,in order to effectively solve these problems,in the research of this thesis,by using different raw materials and synthesis methods,using the vertical growth of MoS₂ nanosheets and the construction of MoS₂ and a variety of materials to form a heterogeneous structure as a strategy,the design and construction of MoS₂-based composite materials The structureactivity relationship between the structure and the performance of the gas sensor,and further focus on regulating the thickness of the MoS₂ layer,the porosity and conductivity of the composite material,and systematically study the NO₂ gas sensing performance of the MoS₂ nanocomposite at room temperature(such as: sensitivity,Response-recovery time,selectivity,stability,etc.).This paper mainly carried out the following work:First,the influence of the porosity and heterojunction of sensitive materials on the gassensing performance is explored.That is,the unique three-dimensional layered structure of porous biomass carbon is used as a template to synthesize MoS₂-WO₃/BC heterojunction nanocomposites by hydrothermal method.The results show that the MoS₂-WO₃/BC composite material has a better sensitivity to NO₂(Ra/Rg = 47.45,100 ppm)and a shorter response time.The detection limit reaches 10 ppb.The excellent performance of the sensor is attributed to the larger porosity and specific surface area;at the same time,the synergistic effect of heterojunction between MoS₂ nanosheets and WO₃ particles is more conducive to carrier transfer and provides more for NO₂ gas adsorption.Active site.Secondly,we explored the influence of the porosity,conductivity and layer thickness of sensitive materials on the gas-sensing performance.Successfully synthesized porous g-C3N4 nanosheets.And through freeze-drying and thermal decomposition,the MoS₂ nanosheets were vertically grown(anchored)on the surface of the porous g-C3N4 nanosheets to construct a three-dimensional MoS₂-g-C3N4 composite material.Thanks to its porous structure,large specific surface area,highly exposed edge active sites,and excellent electrical conductivity,this composite material exhibits excellent room temperature gas sensing performance for NO₂ gas.The sensor shows high response(Ra/Rg= 61.07)and short response/recovery time(2.1s and 35.7 s)to 50 ppm NO₂ gas.The detection limit of the sensor reaches 10 ppb and has long-term stability.Finally,we explored the influence of the thickness of the MoS₂ nanosheets in the sensitive material,the orientation growth direction and the electrical conductivity on the gas-sensing performance.This experiment studies the synthesis of MoS₂ with controllable layer number and growth orientation on the surface of Ti₃C₂T_x MXene with few layers,and further calculation by density functional theory(DFT)reveals that MoS₂-Ti₃C₂T_x MXene(MSMXs)contains Mo or S,respectively.Gas adsorption characteristics at the time of defects.Among them,FV-MSMX(small-layer vertical growth MoS₂-Ti₃C₂T_x MXene)composite material,due to its large surface area,highly exposed vertical edges,appropriate amount of Mo or S defects,and excellent electrical conductivity of the composite material,a large number of Mo-O bonds are formed through the combination between MoS₂ and Ti₃C₂T_x,forming a fast channel for carrier transmission.Therefore,the composite material exhibits excellent gas sensing performance for low concentration NO₂ at room temperature: that is,it has excellent selectivity to NO₂ gas at room temperature,and shows a high response value for 1 ppm NO₂ gas(Ra / Rg = 27.3),and faster response and recovery time(16 s and 45.3 s,respectively).In addition,the detection limit can reach 30 ppb.Has long-term stability and excellent recoverability.