Study On Relationship Between Defect Control And Gas Sensing Properties Of ZnO Nanostructures

As a wide bandgap oxide semiconductor,ZnO is widely used in the field of gas sensing,photocatalysis,wastewater treatment and other related areas because of its unique electrical and optical properties.In particular,ZnO has attracted much attention in the gas sensing applications for its advantages,such as rich morphology,low cost,environmental protection,toxic free and safe.ZnO semiconductor is a type of surface resistance control and the gas sensing response of that depends on the surface structure,so the sheet structure having a large specific surface area and the porous hollow structure contributing to the gas diffusion are both advantageous in improving the gas sensing property.In addition,considering the special transport property and extremely high carrier mobility of graphene oxide(GO),its composite material with ZnO can also exhibit excellent gas sensing properties.The main contents of this paper are as follows:1)Zinc oxide(ZnO)nanosheets with an average thickness of about 20 nm were synthesized directly using a facile precipitation method at room temperature without any template,surfactant or organic solvent.In order to regulate and control the intrinsic surface defect contents,improving the thermal stability,the samples were calcined at different temperatures(200°C,400°C and 600°C respectively);results show that the sheet-like structures can be maintained below 400°C.Photoluminescence(PL)analysis shows that abundant intrinsic surface defects exist on the ZnO-200 surfaces.Gas sensors based on this ZnO-200 nanosheets exhibit high response and good selectivity to acetone vapor at 300°C.Thus,it is considered that the excellent acetone gas sensing property,especially enhanced response value,is mainly originated from the intrinsic defects on the surface of ZnO-200 nanosheets,except for the effect of specific surface area.2)In this chapter,a graphene/ZnO composite system with different content of graphene oxide was prepared by a simple,effective and low-carbon environmental water bath method,and then it was made into device for gas sensing property test.The results showed that ZnO-0.5 GO composite doped with 0.5 mg graphene oxide showed good gas sensing properties to dimethylamine at 200°C.The results revealed that the best compound content of graphene oxide is 0.5 mg,and some donor impurity defects formed by in situ C doping process,which are mainly CZn and Ci.And all of these are conducive to the increase in adsorption of oxygen,thereby enhancing the sensitivity and its sensitivity to 1 ppm dimethylamine at 200 °C can be as high as 4.82.We also found that the n-p conversion of GO/ZnO composites is mainly due to the adsorption that inhibits carrier to transport at low operating temperatures.While the n-p conversion is caused by the decrease in hole concentration that is more important than the increase in electron concentration for the p-type semiconductor at low dimethylamine concentration.3)In this chapter,ZnO hollow microspheres were prepared by sacrificing template at different calcination temperatures,using glucose and zinc chloride as raw materials with two-step method(one-step hydrothermal and two-step calcination).At the same time,in-situ doping of carbon was realized.Gas sensing properties showed that the ZnO-600 hollow microspheres calcined at 600°C exhibited the best gas sensing properties to dimethylamine at the optimum working temperature(240°C).The sensitivity toward 1 ppm dimethylamine can reach 7.21,which has a good application prospect in the field of low concentration dimethylamine detection.It is found that the excellent gas sensing property is due to the combined action of specific surface area and intrinsic defect.It is found that the excellent gas sensing properties are due to the interaction of the specific surface area and the surface defects.