Study On Selective Sensing Mechanism Of NO₂ Gas Based On MoS₂

NO₂ is a common toxic gas,which not only affects the atmospheric environment,but also seriously endangers human health.Therefore,the trace detection of NO₂ is very important for both military and civil fields.As the gas sensor plays an increasingly important role in the intelligent and information society,its market scale is rising rapidly.In addition,the application fields of gas sensors are increasingly extensive,such as environmental protection,aerospace,modern military,chemical and anti-terrorism,automobile industry and so on.It is necessary to study advanced gas sensors because of their wide application field and urgent application demand.Semiconductor gas sensors are one of the most widely used gas sensors.They have the advantages of high sensitivity and fast response.Compared with semiconductor metal oxide,the most widely used commercial sensing material,semiconductor MoS₂ has attracted extensive attention in the field of nano chemical sensing because of its layered structure and wide bandgap.This is because its electrical properties are highly sensitive to external stimuli generated by the surface or interface,which can ensure a high signal response.In summary,considering the great threat of NO₂ gas to the environment and human body,the feasibility of MoS₂ nanomaterials in NO₂ gas sensing is explored.Based on the density functional theory and CASTEP module,the first principles of MoS₂ adsorbed gas molecules were studied.The interaction between different gases（NO₂,CO,H₂,N₂ and NH₃）and MoS₂ was analyzed by the adsorption energy,adsorption distance,bond length of gas molecule,band structure,density of states and electron difference density.The mechanism analysis showed that MoS₂ had excellent selectivity for NO₂.In this project,MoS₂ was synthesized by simple hydrothermal method,and the crystallinity of the material was improved by high temperature annealing.Then the surface morphology and phase of the materials were characterized by SEM,EDS and XRD.The mixture of MoS₂power and C₂H₅OH was ultrasonically crushed and sprayed on the interdigital electrode.The heating resistance wire and interdigital electrode were welded on the sensor base to complete the preparation of sensor.Experimentally,this subject has carried out a gas sensitivity test on NO₂,CO,NH₃,N₂ and H₂ gas.MoS₂ sensor has almost no response to N₂,and the gas sensitivity response of NO₂ is much higher than that of CO,H₂ and NH₃ gas.Theoretical simulation and experimental results has been used to analyze the excellent selectivity to NO₂ gas.A detailed test of NO₂ gas was subsequently carried out,and it was found that the response of sensor increased as the operating temperature increased.The sensor can show a stable gas sensitivity response to different concentrations of NO₂ gas in four response/recovery cycles.The test showed a good linear relationship between gas concentration and the relative response.The sensor sensitivity is 0.85%ppm^-1.The theoretical minimum detection limit is 0.29ppm.The sensor can maintain stable gas sensitivity to NO₂ for 35 days.UV reduced the response/recovery time and significantly improved the response/recovery speed of the sensor.