Synthesis And Gas Sensing Performance Of ZnO-and NiO-based Nanomaterials

In recent years,environmental issues have attracted more and more attention.As an important device for detecting gas types and contents,gas sensors have been widely used in clinical diagnosis of patient breath analysis,vehicle exhaust and industrial exhaust gas detection in environmental protection,national Field detection of poisons in battlefields in safety.The higher the quality of life of the people and the continuous progress of society,the more demand for gas sensors,the stricter the requirements for sensing materials.Metal oxide semiconductor gas-sensitive materials have the advantages of simple preparation method,high sensitivity,low cost,etc.It occupies an important position in gas-sensitive detection,and has attracted wide attention from scientists.However,as a gas sensor,there are still many areas to be improved,such as low sensitivity and poor selectivity.Therefore,in this paper,starting from the synthesis experiments of zinc oxide and nickel oxide semiconductor materials,through the construction of heterostructures and precious metal modification,etc.,the metal oxide semiconductor materials can effectively improve the detection ability of the target gas,and the mechanism of improving the gas sensitivity analysis.The main research contents of this article are as follows:(1)NiO/ZnO microspheres with a diameter of about 2 μm assembled by nanosheets were synthesized by a simple hydrothermal method and a heat treatment process,and their gas-sensitivity properties were tested.The results show that,compared with the pure ZnO microsphere sensor,the response of the nanosheet self-assembled NiO/ZnO microsphere sensor to sulfur dioxide gas has been improved.In particular,the sensor with a Ni/Zn molar ratio of 0.5(0.5 mol%NiO/ZnO)shows high response value(S=107)and superior selectivity to 10 ppm sulfur dioxide at a low operating temperature of 160℃ and the detection limit of the NiO/ZnO sensor toward sulfur dioxide is down to 1 ppm(S=6).The enhanced sensing performance is attributed to the formation of p-n heterojunctions on the interface,the catalytic function of NiO and the three-dimensional microspheres composed of the lamellar structure with a large specific surface area.Three-dimensional microspheres provide more active sites for gas adsorption,and the interlayer gap promotes the diffusion of gas in the three-dimensional structure,so that the material exhibits high sensitivity and excellent selectivity.This work not only provides a simple method for synthesizing NiO/ZnO heterojunction micro spheres with excellent gas-sensing properties,but also provides a gas-sensing material with potential application value in sulfur dioxide gas detection.(2)Combined with the catalytic properties and structural advantages of NiO materials,NiO nanosheets were synthesized,and the gas-sensing properties of the materials were further improved by noble metal modification,and Pt-NiO nanosheets with different concentrations were finally obtained.The NO2 gas-sensitivity test-results of NiO nanosheets before and after modification show that 0.25 mol%Pt-NiO nanosheets have the best gas-sensitivity to nitrogen dioxide,and the response value to 20 ppm nitrogen dioxide at an operating temperature of 160℃ reach 6,response/recovery time is 15/18s respectively,can achieve rapid response and recovery,the detection limit of nitrogen dioxide is also as low as 1 ppm and shows good stability.In addition,0.25 mol%Pt-NiO nanosheets exhibit excellent selectivity to NO2 in complex environments including gases such as SO2,CH4,NH3,and C2H6O.Analysis of its gas-sensing mechanism found that the modification of Pt metal nanoparticles increased the active site of gas adsorption;the catalytic effect of precious metals reduced the activation energy of the reaction,making gas adsorption and redox reactions on the surface of the material more likely to occur,Thereby improving the gas-sensitive performance of the material.