Preparation And Gas-sensing Preformance Of Mxene/Zinc(Cobalt) Oxide Nanocomposites

Atmospheric pollution,as one of the main environmental pollution problems,has always been of great interest to researchers.Among them,VOCs and NO₂,as the main atmospheric pollutants,threaten the ecological environment and have an impact on human health at the same time.Therefore,their detection is of great importance.In the past,metal oxide semiconductor gas sensors have been the mainstay of gas sensing detection research,but their high performance is usually dependent on high operating temperatures.The accompanying high power consumption and safety hazards have become bottlenecks to their development.MXene has excellent conductive properties,tunable electronic structure and large specific surface area,especially its nanocomposite composed with other sensitive materials is considered to have greater application prospects in the field of gas sensors.Therefore,this paper has carried out a study on the preparation of MXene/metal oxide nanocomposites for room temperature sensing.The contents of this paper are as follows:（1）Ti₃C₂Cl₂ MXene and Ti₃C₂Tx MXene were prepared by Lewis acid molten salt method and in situ HF method,respectively,and their electrical performance and gas sensing performance were analyzed.The experimental results showed that the gas sensing elements made of Ti₃C₂Tx MXene prepared by the in situ HF method exhibited higher yield,larger conductivity and less noise at room temperature,and were ideal candidates for use in the preparation of nanocomposites with metal oxides to achieve improved gas sensing properties.（2）Ti₃C₂Tx/ZnO nanocomposites were designed and synthesized by seed layer-induced self-assembly.The results showed that the seed layer was successfully grown on Ti₃C₂Tx MXene nanosheets and in a discrete distribution,and the Ti₃C₂Tx/ZnO nanocomposite induced by the seed layer achieved the detection of NO₂ at room temperature.The nanocomposites inherited the sensitivity of pure phase ZnO to NO₂,exhibiting a 118%response to 10 ppm NO₂ at room temperature with response and recovery times of 63 s and 74 s.The generation of improved gas sensing performance may be attributed to the synergistic effect between Ti₃C₂Tx MXene and ZnO in the composite structure.（3）Ti₃C₂Tx@Co（OH）₂/Co₃O₄ nanocomposites were prepared by an interface induced self-assembly strategy.The high sensing to toluene at room temperature was achieved by tuning its ratios.The response to 100 ppm toluene was improved to 514%with response and recovery times of 9 s and 5 s,respectively.737 times higher than that of Ti₃C₂Tx MXene to 100 ppm toluene gas at room temperature.The energy band structure was analysed in combination with UPS and UV-VIS,and the whole course of its gas sensing reaction was monitored by DRIFTS.The possible adsorption and reaction mechanism of toluene gas at room temperature have been elucidated through the dynamic evolution and equilibrium of its surface adsorbates.The results showed that the high gas sensing performance were attributed to the enhancement effect of the introduction of Ti₃C₂Tx MXene on the heterojunction structure,the electron supplying ability of the Co low orbital in Co（OH）₂ and the promotion of toluene polarization with bond breaking by the high local hole concentration.The design of this composite structure provided a new strategy for the application of Ti₃C₂Tx MXene in the field of gas sensing.