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.