Construction Of Highly Active ZnO/MoS_2(1-x)Se_2x Nanosensing Materials And Gas-sensing Mechanism

The inert base plane of two-dimensional(2D)materials has become one of the main obstacles to improve its gas sensing performance.In order to solve the above problems,in this work,we first synthesized a MoS₂graded material with 2d-in-3d structure by a simple hydrothermal method,and then studied the effects of high temperature atmosphere annealing,heterostructure construction and alloying engineering on its substrate activation and gas sensing properties.This work provides a simple and efficient way to activate,modify and modify MoS₂gas sensing materials.The specific work steps are as follows:(1)The prepared MoS₂graded gas sensing materials were annealed in argon atmosphere at different temperatures(0,550,700 and 850?),and the obtained materials were named S0,S550,S700 and S850 respectively.The S850 sensor has the best gas sensing performance:the response value to 50 ppm NO₂gas at room temperature reaches 623%,the corresponding response time and recovery time are 50 s and 125 s respectively,and the detection limit reaches 20 ppb.In addition,the S850 gas sensor also has good recoverability,selectivity,long-term stability and excellent recyclability under the influence of humidity.High temperature annealing makes MoS₂material produce a large number of s-vacancy defects,and produce strong interlayer coupling and spin orbit coupling effects.(2)MoS₂-ZnO nanocomposites were further prepared by room temperature immersion method to improve the performance of single MoS₂nanomaterials,and MoS₂-ZnO nanocomposites with different composition ratios were prepared by adjusting the concentration of different Zn Cl₂solutions(0.3,0.5,1.0 and 2.0 M).The corresponding samples were named S700-0.3,S700-0.5,S700-1.0,S700-2.0,respectively.The base resistance of the composite material decreases with the increase of the concentration of Zn Cl₂solution.For the gas-sensing performance,with the increase of the concentration of Zn Cl₂solution,the gas-sensing response of the S700 sample gradually increased at first,and the response reached the best when the concentration of Zn Cl₂reached 1.0 M.After further increasing the solution concentration,the gas-sensing response of the material began to decrease.Based on this,the S850-1.0 sample was further prepared,which showed the best gas sensing performance,with a gas sensing response value of 843%to 50 ppm NO₂gas at room temperature,and a theoretical detection limit of 8.1 ppb.And has faster response and recovery time,reaching 40 s and 105 s respectively.(3)MoS_2(1-x)Se_2xnanocomposites with better gas sensing properties were further synthesized by solvothermal method,and the corresponding samples were named as x=0.5%,x=1.5%,x=2.5%,and x=5.1%,respectively.and x=10.2%.Among them,when x=5.1%,the MoS_2(1-x)Se_2xsensor exhibits the best gas sensing performance:the response(R_a/R_g)to 50 ppm NO₂gas at room temperature is greatly improved to 92,and the response and recovery time is only 25 s and 22 s.Compared with MoS₂-ZnO gas-sensing composites,MoS_2(1-x)Se_2xhas more excellent moisture resistance,and when the ambient humidity reaches 83%,the response to 10ppm NO₂atmosphere is still as high as 28(original 42).The improvement of gas sensing performance of MoS₂can be attributed to the activation of S-vacancy defects on its basal plane,the synergistic effect formed by heterostructures,and the effective inhibition of electron-hole pair recombination by the built-in electric field of the alloyed materials.