Preparation Of Zn-modified CuAl-LDHs Materials And Research On NO₂ Gas Sensing Properties

In view of the problems that low concentration NO₂ endangers and affects people's living environment and health,when more metal oxide semiconductors are used as gas sensing materials in the market,they are greatly affected by the environment and the output line is unstable,this paper takes the low-cost layered metal hydroxides(LDHs)as the research object,selects a simple one-step hydrothermal synthesis method,and regulates the proportion and type of metal cations,binary CuAl-LDHs and ternary Cu Zn Al-LDHs nano materials were synthesized by a simple one-step hydrothermal method.The NO₂ gas sensing properties were tested at room temperature,and the gas sensing detection mechanism of the two kinds of materials was preliminarily explored.Firstly,three-dimensional flower like CuAl LDHs materials with ordered stacking of nano sheets were prepared by one-step hydrothermal method by adjusting the proportion of metal cations,using urea as precipitant and pore forming agent and ammonium fluoride as template.The experimental results show that the morphology of CuAl-LDHs is different with the proportion of metal cations.Among the three samples with different proportions,the CA-4 material with the molar ratio of Cu²⁺and Al³⁺of 4:1presents an independent 3D Flower spherical morphology.The thickness of the nano sheet is between 22-28 nm and the smallest size is 6-10?m.When CA-4 is used as a gas sensing element,it shows excellent gas sensing performance for NO₂ at room temperature with relative humidity of 26%.The gas response time is 3.37 s,the detection limit is as low as10 ppb,and it has good repeatability and selectivity.N₂ adsorption-desorption,BJH and XPS experiments show that the large specific surface area,mesoporous structure and more content of defective oxygen of CA-4 sample are the reasons for the improvement of NO₂ gas sensing performance.Furthermore,Cu Zn Al-LDHs nanomaterials modified by nanoparticles were prepared by hydrothermal synthesis by introducing a third metal cation Zn²⁺with similar ion radius.It is found that compared with CuAl-LDHs,the nanosheet of ternary composite Cu Zn Al-LDHs is thinner and the thickness is between 4.04-5.30 nm.The sample size of CZA-2 with a molar ratio of(Cu²⁺+Zn²⁺):Al³⁺is 2:1 was optimized to 3-5?m.The pore size on the nanosheets is concentrated at 2.37 nm.The test results of NO₂ gas sensing performance of Cu Zn Al-LDHs with different molar ratios at room temperature show that CZA-2 nanomaterial has the best gas sensing performance,and shows good response sensitivity and stability to 100 ppm NO₂.The gas sensing response is 22.30,the response time is 2.66 s,and the detection limit is 30 ppb.The reason is that the thin porous structure can reduce the electron transmission resistance and increase the carrier density;at the same time,the nanoparticles attached to the thin layer become the active sites of the reaction,which improves the gas sensing performance of ternary LDHs materials,and it has a certain theoretical significance for the practical application of LDHs materials in the field of gas sensing.