Preparation Of Low Dimensional Narrow Band Gap TiO₂ And ZnO Composites And Their Photocatalytic Properties

Nowadays, developing clean and efficient renewable energy sources is urgent tasks. Solar energy is a kind of omnipresent, inexhaustible natural energy source. The application of photocatalysis with photoelectric functional semiconductor is a kind of environmentally friendly method with clean energy which can decompose water to hydrogen. In the same time, photoelectric functional semiconductor completely decomposes the organic pollutants under the solar light. Therefore, studying photoelectric functional semiconductor is regarded as a potential solution to alleviate the tension of enery and implement environmental restoration.TiO₂ and ZnO are two kinds of common nanometer semiconductor materials which possess photoelectric function. Researchers are always interested in them. But these conventional materials have a lot of limitations in practical application.They mainly absorb and utilize UV-light which accont for a little part of sun light,and have a relatively low visible light response of the main part of the solar spectrum. Therefore, reducing the band gap of TiO₂ and ZnO makes full use of the visible light range of sunlight, which has a practical significance.Element doping has influences on the material’s band level resulting in changing the photogenerated charges transport properties. Some metal or nonmetal elements have been doped to adjust the electronic structure and enhance the photocatalytic activity of photoelectric functional semiconductor by chemical methods or physical methods. However, Elements doping can lead to unstable thermal or crystal instability and increased the charge-carrier trapping.This could reduce the photocatalytic efficiency.More importantly, most of the traditional modified methods need higher temperature or complicated and expensive equipment, so it’s almost difficult for people to apply the traditional methods to industrial production and other semiconductors’modification. So, we can use appropriate modified methods or synthesize heterostructure semiconductor material to solve the problems which make the conventional materials to have better photovoltaic effect. In a word, using simple processing method or narrow band gap heterostructure semiconductor to modify TiO₂ and ZnO and other wide band gap semiconductors is an important way to improve their photoelectric activity.Bases on above reasons, this research work include:（1） Mesoporous TiO₂ microspheres were synthesized by the moderating hydrothermal process and then put into a vacuum oven for different hours（2h,4h,6h,8h）, resulting in Ti3+self-doped.Their morphology was characterizated by X-ray diffraction （XRD）, UV-Vis absorption spectroscopy and transmission electron microscopy （TEM）.The influence of high temperature vacuum treatment for visible-light response and catalytic properties was tested by the experiments of photocatalytic degradation RHB under visible light and UV-Vis absorption. The water oxidation spectrum and photocurrent test figure out the quantity of photogenerated charges and the transport mechanism of the five samples. Then compared and discussed the samples in order to know the best processing time. Finally we explored the reason of photoelectric superior performance by XPS and Mott-Schottky curves.（2）Firstly, we synthesize the ZnO nanorod （NR） arrays on F-doped SnO2 glass.Then used a novel ion exchange method to prepare ZnO/ZnS, ZnO/CdS and ZnO/Ag2S heterogeneous nanorod （NR） arrays. The morphology of the four samples were characterized and the change of morphology was observed. The photoelectric currents and photocatalytic water oxidation experiments of these heterostructures were investigated in detail under simulated sunlight （AM1.5） in comparison with fresh ZnO NRs. In addition, the theoretical analysis of the photoelectric effect is discussed according to the result of Mott-Schottky curves. This shows that the three chalcogenides semiconductors have good visible-light induced the photoelectric effect. The results of photoelectrochemical water decomposition experiments show that the ZnO/ZnS photo anode has a minimum starting voltage and ZnO/Ag2S photoanode possesses the highest photocurrent under simulated sunlight. Mott-Schottky curves show that the position of the energy band is related to the initial water oxidation voltage which is from photoelectric chemical decomposition water measurement.