| It is well-known that photocatalytic hydrogen production from water splitting under the sunlight irradiation has broad application prospect in the field of environmental and energy. However, the photocatalyst will be one of the key factors in the practical applied of photocatalytic reaction. In the past 40 years, the researchers at home and abroad made a lot of in-depth study on photocatalytic material and their catalytic activity of hydrogen production. They have found many semiconductor materials that have excellent catalytic properties, such as Ti O2, Cd S, Zn S, Na Ta O3 and KNb O3. But they have a serious drawback: their forbidden band gap is too wide, which will lead to only absorb ultraviolet light of the sunlight. However, the content of uv-light accounts for only 5.0% of the total sunlight, leading to the extremely low sunlight utilization rate. The research on the new type of visible light induced catalyst has increasingly becomes the focus of domestic and foreign scientists in order to improve the practical application value in the field of photocatalytic hydrogen production from water splitting under the sunlight irradiation.In recent years, we have been engaged in the study of Ti O2 combined with up-conversion luminescence agents to perform the visible-light photocatalytic degradation of organic pollutants and the visible-light photocatalytic hydrogen production from water splitting. We found that the photocatalytic activity of Ti O2 has been greatly improved. It can be attributed to the up-conversion luminescence materials which have the properties of emitting the high energy ultraviolet-light by absorbing the low energy visible-light. And they can provide more ultraviolet-light for Ti O2. However, the relatively high reduction potential of Ti O2 usually leads to lower photocatalytic reaction rate. In order to maintain a higher photocatalytic activity and photocatalytic reaction rate, we need to choose a broadband gap of semiconductor materials with lower reduction potential as catalyst combined with up-conversion luminescence agents for studying photocatalytic hydrogen production from water splitting.In this study, we choose Na Ta O3 as catalyst and make a series of researches on the application of up-conversion luminescence agent-Na Ta O3-cocatalysts system in hydrogen production from water splitting and research of related influential factors. Na Ta O3 was synthesized by hydrothermal method. Er3+:YAl O3 and Er3+:Y3Al5O12 were synthesized by sol-gel method and Tm3+,Yb3+:Na YF4 was prepared by hydrothermal process. The corresponding visible-light photocatalysts, Er3+:YAl O3/Pt-Na Ta O3, Er3+:YAl O3/Cu O- Na Ta O3, Er3+:YAl O3/Mo S2-Na Ta O3 and Tm3+,Yb3+:Na YF4-Er3+:Y3Al5O12/Mo S2-Na Ta O3 composites were successfully prepared by particle mixing and coating methods. For comparison, these photocatalysts are all characterized by X-ray diffractometer(XRD), scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDX), excitation spectrum and emission spectrum. And then, the influential factors such as up-conversion luminescence materials and Na Ta O3 mass ratio, heat-treated temperature, heat-treated time and initial p H value on the visible-light photocatalytic hydrogen production activity of Er3+:YAl O3/Pt-Na Ta O3, Er3+:YAl O3/Cu O-Na Ta O3, Er3+:YAl O3/ Mo S2-Na Ta O3 and Tm3+,Yb3+:Na YF4-Er3+:Y3Al5O12/Mo S2-Na Ta O3 composites are investigated.Through the research on the preparation methods and properties of Na Ta O3, up-conversion luminescence agent-cocatalyst system, we find that the method of up-conversion luminescence agent combining with traditional photocatalysts and loading the appropriate cocatalyst to prepare new photocatalysts can not only improve the utilization efficiency of sunlight but also provide a new way for large-scale hydrogen production in the future. |
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