| As we all known, hydrogen is now considered to be an ideal future energy and the photocatalytic water splitting to produce hydrogen becomes an important subject in the storage and conversion of solar energy. Among all the photocatalysts, ZnO have been considered to be an potential photocatalyst and extensively explored for solar energy conversion because it possesses an energy band structure and optoelectronic properties similar to those of TiO2, while has a higher electron mobility, easier crystallization and anisotropic growth. Especially, the ZnO nanostructure with high length-diameter ratio has been drew more attention due to its more excellent electron transport ability and bigger specific area than ZnO nanoparticles. However, Zinc oxide is broadband gap semiconductor, and only has absorption in the UV area, which will limit its practical application. The present studies showed that dye sensitization is one of the most efficient ways for broadening the photocatalyst in the visible area. Therefore, dye sensitized ZnO nanostructures with high surface to volume could be an efficient visible-light-driven photocatalyst. And it can solve the problem of immobilization of nanomaterials, such as decrease of specific surface area and photocatalytic activity. Based on the above ideas, we report a series of dye sensitized ZnO "nanograss" photocatalysts and made a system exploration of photocatalytic hydrogen production activity. The main contents are as follows:(1) We carried on a systematic study on low temperature hydrothermal method for preparation of ZnO "nanograss" and discussed the effects of experimental conditions such as hydrothermal temperature, hydrothermal time and concentration precursor solution on morphology and crystal structure of ZnO "nanograss".(2) We fabricated a photocatalytic system of Eosin Y sensitized ZnO "nanograss". With triethanolamine (TEOA) as sacrifice agent, we studied its photocatalytic activity for water splitting under the visible light. Furthermore, we researched properties of dye and mechanism of hydrogen production by the ways of optical and photoelectrochemistry respectively. The results indicate that this photocatalytic system proved to be an efficient visible-light-driven photocatalyst with high photocatalytic activity and a rate of H2 evolution of approximately 0.46 L m-2 h-1 was achieved. In addition, the results also show that the fabrication of dye sensitized ZnO "nanograss" can solve the decline of the catalytic activity which caused by immobilization of nanomaterials.The photocatalytic activity of Eosin Y sensitized ZnO "nanograss" is 1.26 times higher than that of the Eosin Y sensitized ZnO nanoparticles.(3)A more efficiently immobilized photocatalyst for visible light-induced H2 evolution was constructed on ZnO "nanograss" cosensitized by Eosin Y (EY) and Rose Bengal (RB). By studying the factors such as mixing proportion and dye concentration of two kinds of dyes on catalytic activity of hydrogen production, we get the best photocatalytic system for hydrogen evolution. The results indicated that there exist a strong synergy between EY and RB. Under the same conditions, the cosensitized system showed an obviously advantage over single dye sensitized system. The visible photocatalytic activity of cosensitized ZnO "nanograss" achieved a maximum H2 evolution of 0.52 L m-1h-1 which was 130% and 58% higher than that of single EY and RB sensitized system, respectively. Besides, we also studied mechanism of synergy between EY and RB by means of optical and photoelectrochemistry. The results suggested that the synergy was mainly from the effective Forster resonant energy transfer produced between two dyes. |
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