The Synergistic Effects of Two Co-catalysts on Zn 2 GeO 4 on Photocatalytic Water Splitting
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The Synergistic Effects of Two Co-catalysts on Zn2GeO4 on Photocatalytic Water Splitting Baojun Ma • Fuyu Wen • Hongfu Jiang • Jinhui Yang Pinliang Ying • Can Li
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Received: 3 October 2009 / Accepted: 6 November 2009 / Published online: 21 November 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Zinc orthogermanate was prepared via a hydrothermal method and a remarkable synergistic effect on the photocatalytic activity for overall water splitting was found for Zn2GeO4 co-loaded with noble metals (Pt, Rh, Pd, Au) and metal oxides (RuO2, IrO2). The photocatalytic activity of Pt-RuO2/Zn2GeO4 for overall water splitting is 2.2 times of Pt/Zn2GeO4 and 3.3 times of RuO2/Zn2GeO4. Photocatalytic half reactions evaluation of water splitting for H2 and O2 productions shows that Pt plays the major roles in H2 production and RuO2 promotes the O2 production. The roles and valence states of co-catalysts and the mechanism of photocatalytic reaction are discussed. Keywords Synergistic effect Pt and RuO2 co-catalysts Zn2GeO4 Overall water splitting
1 Introduction In the last three decades, the photocatalytic production of H2 via water splitting over semiconductor photocatalyst has received considerable attention [1–21]. Recently, Ge4? containing compounds including oxides [22], nitrides [23], or oxynitrides [24] have attracted considerable interests
Electronic supplementary material The online version of this article (doi:10.1007/s10562-009-0220-8) contains supplementary material, which is available to authorized users. B. Ma F. Wen H. Jiang J. Yang P. Ying C. Li (&) State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, P.O. Box 110, 116023 Dalian, China e-mail: [email protected] URL: http//www.canli.dicp.ac.cn
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due to their unique photocatalytic properties for water splitting. An interesting example is zinc orthogermanate, Zn2GeO4, which is not only a sort of glass or ceramic having special optical properties [25] but also an efficient photocatalyst [22]. Sato et al. [22] synthesized Zn2GeO4 via high-temperature solid state reaction (SSR) and used the RuO2/Zn2GeO4 for water splitting. They investigated the effect of calcination temperatures on photoactivity and calculated the band structure of Zn2GeO4 by DFT. It appears that co-catalyst may play a crucial role in water splitting on the photocatalysts. However, the roles of cocatalysts played in the photocatalytic overall water splitting have not been well investigated. The photocatalytic activity of a photocatalyst depends on not only its intrinsic properties [26] such as the photoabsorption [27], positions of the valence band and conduction band [28], but also the co-catalysts [29, 30]. Appropriate co-catalysts are able to trap electrons or holes, reduce the possibility of electron–hole recombination, catalyze the reactions and therefore increase the photocatalytic activity. RuO2 is a well-known oxidation catalyst for O2 evolution. In the case of water splitting, RuO2 has been demonstrated to be an e
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