Research Of NO₂ Gas Sensor Based On ZnO Nanomaterials

NO₂ is a main pollution gas in the air atmosphere.If there is excess NO₂ gas in the environment,it will cause detrimental phenomena such as acid rain and photochemical smog.In view of human health,if one person inhales too much NO₂,it will cause damage to the lungs,eyes,respiratory tract.In order to avoid the above hazards,it is necessary to accurately detect the concentration of NO₂ in the atmosphere to control its emission and maintain the health of the environment and ecology.Gas sensors can detect the concentration of harmful gases and play the role of monitoring their emission.Gas sensors based on oxide semiconductors are widely concerned by researchers because of their low cost and simple operation.Zinc oxide is a stable n-type semiconductor with a direct bandgap.It has the properties of is a low dielectric constant,excellent electrical properties,and non-toxicity.It has gained wide concern in the field of gas sensor.However,when pristine ZnO material is used as a gas sensing material for gas detection,its response value,selectivity and response/recovery characteristics can not completely satisfy the requirement of realistic applications.In order to improve the gas sensing performance of ZnO based sensor,the heterojunction construction with ZnS,and functionalizion with noble metal Pd were adopted respectively.The details are as follows:1.ZnS/ZnO composites were synthesized by two-step solvothermal and hydrothermal methods,and ZnS particles with a diameter of about 20 nm were grown on ZnO nanowires.The gas sensing test results show that when the composite ratio of ZnS/ZnO is equal to1/3,the sensitive material has the best gas sensing performance to NO₂ gas,and the response value to 2 ppm NO₂ gas at 137.5?is 36.88.Which is 1.5times higher than that of pure ZnO nanowires.ZnS/ZnO based sensor also exhibits excellent lower detection limit and better reproducibility performance.The heterocomposite structure modulates the energy band structure,carrier concentration,and specific surface area of the material,which plays a positive role in improving the gas sensing performance of the sensor.2.Pd-ZnO nanowires with different loading amount of Pd were synthesized by solvothermal method and subsequent Pd loading process via reducing Pdl₂.The microstructure characterization shows that ZnO has a wire-like microstructure,and the noble metal Pd nanoparticles with a diameter of 3-5 nm are distributed on the surface of the ZnO nanowires.Gas sensitivity test results show that when the Pd loading amount is 1wt%,the sensitive material has the best gas sensing performance to NO₂ gas.The sensor has a response of 179.12 to 2 ppm NO₂ gas at 137.5°C,which is about 7 times of pure ZnO material.Its response and recovery time are 47 and 49 s and low detection limit is 10ppb.Pd loading greatly improves the gas sensing performance of the sensor.The performance improvement is mainly due to the synergistic effect of the spillover effect and chemical sensitization when the precious metal Pd is loaded on the surface of ZnO.