Modifying Of ZnO-Based Semiconductor Materials And Their Photoelectrochemical Properties Research

ZnO is important photoelectric functional material as a kind of wide bandgap semiconductor.In this thesis,ZnO with different structure and morphology are synthesized by various methods.The generated ZnO are modified in order to improve the photoelectrochemical properties.The structure and morphology of the obtained ZnO are characterized,the photoelectrochemical property and photocatalytic activity are researched,and the mechanism are discussed in the followed three parts:(1)It is demonstrated that a novel and facile two-step strategy for large scale synthesis of Se-doped ZnO nanoplates by combining mechanical alloying with annealing process,in which ZnSe nanocrystals were firstly prepared via a mechanical alloying method,and followed by annealing process in air to incorporate Se as a dopant in ZnO to form Se-doped ZnO nanoplates.X-ray diffraction and high resolution transmission electron microscope studies indicate that the as-fabricated Se-doped ZnO is the wurtzite ZnO structure.X-ray photoelectron spectroscope and Raman results reveal that Se is successfully doped into ZnO.UV-vis absorption spectra of the Se-doped ZnO nanoplates reveal the significantly enhanced light absorbance compared with undoped ZnO nanocrystals.Room temperature photoluminescence spectra indicate that recombination of photogenerated charge carriers for Se-doped ZnO nanoplates is inhibited significantly.The achieved Se-doped ZnO nanoplates show remarkably enhanced photoelectrochemical(PEC)and photocatalytic degradation activity.The photocurrent density of Se-doped ZnO nanoplates reaches up to?0.2 m A/cm²,which is significantly larger than that of undoped ZnO nanocrystals(?0.015 m A/cm²).The photodegradation of methylene blue dye in 2.5 h over Se-doped ZnO nanoplates is about 94.5%,which is significantly enhanced to the undoped ZnO nanocrystals(59.4%).Furthermore,Se-doped ZnO nanoplates show high stability after being used for photocatalytic degradation organic dye during 4 cycles.(2)The core-shell structures are designed to take advantages of each material to improve the PEC performance.Here we report a facile ion-replacement strategy for fabricating ZnO/ZnSe/Cd Se/Cu_2-xSe core-shell nanowire arrays grown on Fluorine-doped tin oxide(FTO)glass under hydrothermal conditions.Under illumination with AM 1.5G,the designed ZnO/ZnSe/Cd Se/Cu_2-xSe core-shell nanowire arrays exhibit superior PEC performance with the highest photocurrent density of 20.57 m A/cm²,which is 29.4 times higher than that of the ZnO nanowire arrays at 0 V versus Ag/Ag Cl,and achieve the incident photon conversion efficiency of 87.6%at 410 nm without applying bias potential.The superior PEC performance of the ZnO/ZnSe/Cd Se/Cu_2-xSe core-shell nanowire arrays results from the synergistic effects of each material.Vertical aligned ZnO hexagonal prisms provided large specific surface area and electron access along the axial direction.ZnSe layer further extended specific surface area and the range of light absorption.Cd Se layer enhanced the visible light absorption vastly and fully utilized the incident light.P-type Cu_2-xSe layer produced p-n junctions,which could not only prevent the recombination,but also promote the separation and transmission of photo-generated electron-hole pairs.The synergistic action of each component in ZnO/ZnSe/Cd Se/Cu_2-xSe core-shell nanowire arrays led an outstanding PEC performance,which can have promising applications for designing highly efficient electrodes of other materials for water splitting.(3)ZnO-CuS core-shell nanotube arrays are prepared combined electrochemical deposition method and successive ionic layer adsorption and reaction method.ZnO nanotube arrays are synthesized on FTO glass via a two-step electrochemical deposition method.CuS nanoparticals are then produced on the surface of ZnO nanotubes by successive ionic layer adsorption and reaction method.Under visible light,the photocurrent density of ZnO-CuS core-shell nanotube arrays reaches 21.18?A/cm²,which is 14.9 times higher than that of the ZnO nanorod arrays at 0 V versus Ag/Ag Cl.Vertical aligned ZnO nanotube arrays provided large specific surface area and electron access along the axial direction.The well matched bandgap structure is beneficial to the separation and transmission of photo-generated electron-hole pairs.P-n junction at interfaces promotes the conversion efficiency of photo-generated electrons,which improves PEC property of ZnO-CuS core-shell nanotube arrays.