Synthesis And The Photoelectric Properties Of One-dimensional ZnO/ZnS Core-shell Nanowires

As a direct wide band-gap(3.37 eV)semiconductor,zinc oxide(ZnO)nanostructures are important and extensively studied for their outstanding electric and optical properties.Especially the excitonic binding energy of ZnO(60 meV)is very large so it has efficient exciton emission at room temperature.This feature makes ZnO one of the suitable materials for blue/ultraviolet(UV)optoelectronic devices.It is reported that ZnO nanostructures have potentials in various applications,including sensing applications,field effect transistors,solar cell electrodes and nanogenerators etc.Especially vertically aligned ZnO nanowire arrays have drawn considerable interest because of their one-dimensional structure and unique properties.In these applications,how to control the growth condition to obtain ZnO nanowire arrays with designed morphology and quality is the key problem to improve the performance of these devices.When they are combined as ZnO core/ZnS shell nano wires,the ZnS shell acts as a functional barrier between ZnO and the ambient which dramatically alters the properties of core nanowires.Therefore,ZnO@ZnS core-shell nanowires have been reported to present improved physical and chemical properties in different applications,including excellent photoluminescence,enhanced conversion efficiency in dye-sensitized solar cells,etc.The mainly results are summarized as follows:(1)Vertically ordered and well crystallized long ZnO nano wire arrays were synthesized on FTO glass substrate by a microwave-assisted hydrothermal method.Super-long ZnO nano wire arrays on FTO glass substrate have been obtained in a rather short time by using a self-made continuously dropping setup.The researches show that the length of the nanowire arrays can be lengthened incessantly by extending the growth time.By comparing the morphology and length-diameter ratio of those ZnO nanowire arrays.which are synthesized with different concentration ratio of zinc salt.It can be seen that zinc acetate is a rather ideal zinc source for the fast growth of nanowires with optimal morphology.(2)Vertically ordered and well crystallized long ZnO nanowire arrays were synthesized by zinc acetate.To demonstrate the photocatalystic activity of ZnO nanowires,MO is chosen as representative organic dyes to evaluate the photo catalytic performance.The degradation rate of MO solution increases with the length of aligned ZnO nanowire arrays.In this work,nanowires can provide a fast channel for electron transportation,so undesirable recombination can be prevented effectively.On the other hand,with the elongate of those nanowires,the increased surface defect could serve as trappers of the electrons or holes to restrain their recombination.The space between nanowires is considered to be the ideal place for the pollutants adsorption.Due to the above reasons,these longer ZnO nanowire arrays present good photocatalytic performance.(3)Aligned ZnO@ZnS core-shell nanowire arrays are synthesized on FTO glass substrate by sulfurizing ZnO nanowires using vapor phase method.These ZnO@ZnS nanowires are well-crystallized and highly oriented in c-axis direction.The thickness of the ZnS shell can be controlled by adjusting the reaction time.The result indicates that when used to decompose methyl orange(MO),the core-shell nanowire arrays have superior photocatalytic performance under UV-light irradiation,which shows considerable potential applications of this nanocomposite in water purification.