Preparation And Gas Sensing Performance Of SnO₂@ZnO Composites

With the improvement of living standards,people gradually realize the importance of the living environment,and the monitoring of toxic and harmful gases has become more and more important.NO₂ is a kind of nitrogen oxides,which can be produced by human production activities and natural phenomena.Excessive levels of NO₂ can cause a variety of environmental problems,such as acid rain,surface water acidification,eutrophication,and reduced atmospheric visibility.When NO₂ is inhaled by the human body,it can cause strong irritation and corrosion to the lung tissue and endanger human health.Based on the previous literature reports and previous researches,SnO₂@ZnO composites is prepared by two-step microwave-assisted hydrothermal method.The composites were analyzed for their growth mechanism and their gas sensing properties were systematically studied.The response properties of SnO₂@ZnO composites doped with different metal elements to NO₂ gas were also investigated.The main research contents are as follows:First,ZnO nanorods were prepared as primary materials by microwave-assisted hydrothermal method.On this basis,the SnO₂@ZnO composite was prepared by secondary microwave assisted hydrothermal method.Through orthogonal experiment and range analysis,the responsiveness of 10ppm NO₂ gas at 300°C was used as the index to determine the primary and secondary factors affecting the gas sensitivity of SnO₂@ZnO composites.The crystal structures and microstructures of SnO₂@ZnO composites prepared under optimized preparation conditions were characterized by XRD,SEM,EDS and XPS.Finally,the growth mechanism was explored by time single factor experiment.Based on the optimization of process parameters,the effects of different concentrations of metallic elements Ni,Cu,La and Mn on the microstructure and morphology of SnO₂@ZnO composites were investigated.XRD,SEM and EDS were used to test the characterization methods.The doped SnO₂@ZnO composites were systematically analyzed.The results show that when the doping concentration is 1%,the four elements are undoped successfully.When the doping concentration is 3%,only Cu is doped.The impurity is successful,and when the doping concentration is 5%,all four elements can be doped successfully.As the doping concentration of the element increases,the morphology of the SnO₂@ZnO composite is changed,SnO₂ preferentially grows into a sheet structure on the surface of ZnO.Finally,the gas sensing properties of the prepared composites were systematically investigated.The results show that SnO₂@ZnO composites have low operating temperature,high responsiveness,fast response/recovery time,and composite materials compared with single ZnO nanomaterials.Good selectivity and repeatability for NO₂ gas.After adding 5%concentration of Ni and Cu elements,the responsivity of SnO₂@ZnO composites is significantly improved,while the performance after adding 5%concentration of La and Mn elements is decreased.Finally,the gas sensing mechanism of SnO₂@ZnO composites was theoretically analyzed based on the experimental results.