Preparation And Acetone Gas Sensing Property Study Of ZnO Nanocomposite

As a kind of wide band gap N-type semiconductor,ZnO semiconductor materials are one of the most common metal oxide semiconductor materials in the field of gas sensors because of their stable physical and chemical properties,abundant sources,low cost,and easy preparation.However,ZnO-based gas sensors have many disadvantages:high operating temperature,poor selectivity,low stability,which limits its market and large-scale development.At present,doping modification is one of the most commonly used methods to improve the gas sensitivity of ZnO.In this project,CuO-ZnO nano-powders with different doping concentration were prepared by sol-gel method.The samples were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,X-ray energy dispersive spectroscopy?EDS?and N₂adsorption-desorption.The gas sensing properties of the samples were tested by Gas Sensing Test System.The effects of doping concentration,annealing temperature,operating temperature,relative humidity,visible and ultraviolet light excitation on the gas sensing properties of the sensor were investigated.From the results of XRD,SEM,EDS and N₂ adsorption-desorption,it can be seen that ZnO is mainly hexagonal wurtzite structure,and some ZnO were contected with monoclinic phase CuO.The doping of CuO led to the porous surface and small gain size of ZnO.The specific surface area and the porosity of the samples are the largest when the annealing temperature is 500?.The operating temperature changes the sensor's sensitivity to acetone and the optimum operating temperature of the CuO-ZnO semiconductor is 30?.In addition,the sensor has the best selectivity for acetone when the operating temperature is 30?,however,the selectivity to toluene and formaldehyde reaches the optimum when the operating temperature is near 100?.Visible light excitation and UV excitation also have an influence on the gas sensing properties of the sensor.The results show that the visible light and ultraviolet light both can enhance the gas sensing properties of CuO-ZnO,and the enhancement of UV light is more significant than that of visible light.Under ultraviolet light,the sensitivity of CuO-ZnO with 4.17 at%doping to 500 ppm acetone was 253.16,about 1.3 times that under visible light irradiation and about 2.4 times that under dark conditions.In addition,under the dark conditions,the highest gas sensing response was obtained when the relative humidity was30%RH,but the gas sensing response was the best when the relative humidity was 50%RH under UV light irradiation.This may be the ZnO surface water vapor photolysis related.The band gap of CuO-ZnO nanomaterials was calculated from the UV-Vis spectra.The results show that the band gap of ZnO decreases from 3.22eV to 2.97eV after CuO doping,which is beneficial to enlarge the absorption range of visible light,increase the light utilization efficiency and decrease the operating temperature.Finally,the gas-sensing mechanism is discussed using semiconductor surface conductance control models and grain boundary barrier theoretical models combined with photocatalytic theory.