Synthesis Of ZnO Based Nanocomposites And Their Gas Sensing Properties

ZnO is a typical n-type metal oxide semiconductor.Owing to its excellent physical and chemical performances,ZnO has been widely investigatied as gas-sensing mateirals in the field of gas sensor.In order to enhance gas-sensing properties of ZnO,surface morphological modification and construction of composites with other oxides are both effective methods.As a result,in this work,several unique hierarchical structures of ZnO and Ni O/ZnO composites were synthesized,and their phase structures and morphologies were characterized via XRD,SEM,EDS,TEM and etc.The morphological evolution mechanism and enhancement mechanism for ethanol gas-sensing properties were studied.(1)Three-dimensional hierarchical ZnO nanoflowers were successfully synthesized via a hydrothermal route assisted by surfactant CTAB serving as template and stabilizer.In addition,low-dimensional ZnO nanoparticles and nanoplates were also prepared hydrothermally.Morphological characterization reveals that the nanoparticals and nanoplates show severe agglomeration,while the hierarchical nanoflowers assembled by nanosheets have uniform size,good dispersion and a large number of pores,which greatly facilitates the adsorption and diffusion of ethanol molecules.Among all the nanostructures,the nanoplates-assembled nanoflowers exhibites significantly higher ethanol gas-sensing performances than the others.Furthermore,it is found that the concentration of surfactant CTAB has an essential effect on the ultimate morphology of the hierarchical nanoflowers,and finally its possible growth mechanism is dicussed.(2)Based on the above hydrothermal synthesis of pure ZnO,hierarchical flowerlike Ni O/ZnO composite was successfully prepared using a simple and efficient one-step hydrothermal method through introducing a nickel source.Such flower-like structure is consisted of numerous nanosheets.It is found that the nanosheet-assembled flower-like Ni O/ZnO composites display excellent ethanol gas-sensing properties as compared to pure ZnO nanostructures based gas sensor,which may ascribe to its unique hierarchical architectures and the formation of p-n heterojunction at the interface between p-type Ni O and n-type ZnO.Additionally,possible growth mechanism of hierarchical flower-like composite is preliminary dicussed.(3)Hierarchical Ni O/ZnO hollow spheres composites were triumphantly synthesized through a glycine assited hydrothermal route.The measured results demonstrate that the hollow Ni O/ZnO hierarchical heterostructures based sensor exhibits outstanding ethanol gas sensing performances with lower operating temperature,superior gas response and excellent repeatability.This is mainly because the hierarchical hollow sphere structure has rough outer and inner surface as well as a large number of pores,which may offer sufficient active sites and gas diffusion channels for surface sensing reaction.Moreover,the formation of p-n heterojunction between p-type Ni O and n-type ZnO regulates the carrier concentration of materials.Finally,possible morphological evolution mechanism of hierarchical hollow sphere is successively dicussed.The formation of hierarchical hollow sphere is mainly due to glycine as a spherical sacrificial template,which acts as a structure director.