Nanosized Au Particles as an Efficient Cocatalyst for Photocatalytic Overall Water Splitting
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Catalysis Letters Vol. 108, Nos. 1–2, April 2006 (Ó 2006) DOI: 10.1007/s10562-006-0030-1
Nanosized Au particles as an efficient cocatalyst for photocatalytic overall water splitting Akihide Iwasea, Hideki Katoa, and Akihiko Kudoa,b,* a
Department of Applied Chemistry, Faculty of Science, Science University of Tokyo, 1-3 Kagurazaka, Shinjyuku-ku, Tokyo 162-8601, Japan b Core Research for Evolutional Science and Technology, Japan Science and Technology Agency (CREST, JST), Japan
Received 1 November 2005; accepted 5 January 2006
The effect of the photodeposition of gold particles onto several photocatalysts on the photocatalytic activities was studied. The photocatalytic activities of K4Nb6O17, Sr2Nb2O7, KTaO3 NaTaO3, and NaTaO3 doped with La for water splitting were improved when gold particles were deposited. The latter were nanoparticles, consistent with their surface plasmon absorption. The nanosized gold particle functioned as an efficient cocatalyst for photocatalytic water splitting by assisting H2 evolution. KEY WORDS: nanosized Au catalyst; photocatalysis; water splitting.
1. Introduction Development of an energy system based on H2, which is an ultimately clean form of energy, has been urged. Photocatalytic water splitting into H2 and O2 has drawn attention as one of the attractive H2 production technologies. Many highly active metal oxide photocatalysts have been reported for water splitting under UV irradiation [1–3]. Titanate and niobate photocatalysts for water splitting usually require cocatalysts, because they lack active sites for H2 evolution on their surfaces [1]. Although many unmodified tantalate photocatalysts are active for overall water splitting, their activities are drastically improved by loading with NiO cocatalysts [4]. Thus, the cocatalyst is indispensable for photocatalysts for highly efficient water splitting. Noble metals such as Pt [5–7] and Rh [8, 9], and oxides such as NiO [10], RuO2 [3, 11], and IrO2 [12] have been reported to be effective cocatalysts for photocatalytic water splitting. However, the well-known cocatalyst Pt is not ideal for overall water splitting, because the back-reaction between evolved H2 and O2 to produce water proceeds efficiently on the surface. Moreover, the number of cocatalyst materials is still limited, even though they play quite important roles in photocatalytic water splitting. Therefore, the further development of effective cocatalysts is important. Gold had generally been regarded as an inactive metal. However, since Haruta et al. discovered that nanosized gold particles loaded on TiO2 exhibit high activity for catalytic oxidation of CO [13, 14], the catalytic peformance of nanosized gold particles has been
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extensively studied [14]. Kamat et al. and Calzaferri et al. have found that photocurrents at TiO2 [15] and AgCl electrodes [16] were improved by modification with nanosized gold particles. Au-loaded photocatalysts for the decomposition of nitrate ions [17], azo-dyes [18], and perchlorinated compound [19]
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