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MATERIALS RESEARCH

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Preparation of a high active photocatalyst, K2 La2 Ti3 O10 , by polymerized complex method and its photocatalytic activity of water splitting Shigeru Ikeda, Michikazu Hara, Junko N. Kondo, and Kazunari Domena) Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan

Hiroyuki Takahashi, Toru Okubo, and Masato Kakihana Materials and Structure Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan (Received 17 September 1997; accepted 16 December 1997)

A layered perovskite type oxide, K2 La2 Ti3 O10 , was prepared by a gel technique using the polymerized complex (PC) method. A single phase K2 La2 Ti3 O10 was obtained by adding twice the potassium required for stoichiometry. The Ni–K2 La2 Ti3 O10 catalyst prepared by the PC method exhibited a higher photocatalytic activity for decomposition of H2 O into H2 and O2 than that prepared by a conventional solid state reaction.

I. INTRODUCTION

Photocatalytic decomposition of water over semiconductor powders is an attractive system to convert photon energy into chemical energy.1–16 We have demonstrated that layered ion-exchangeable oxides exhibit especially high photocatalytic activity by making use of the interlayer spaces as the reaction sites; A4 Nb6 O17 (A ­ K, Rb) with Ni or Pt loading and Ni-loaded A2 La2 Ti3 O10 (A ­ K, Rb, Cs) powder can decompose water into H2 and O2 efficiently.3–7,14–16 In general, these layered photocatalysts are prepared by calcination of the mixtures of appropriate amounts of metal oxides or carbonates, which is the so-called solid state reaction method. This preparation method requires repeated grinding and long heating time at high temperatures to allow interdiffusion of cations. The particle sizes of the powders produced by the method are not uniform, and the appearance of a nonstoichiometric part is also frequently inevitable. To control the particle size, the wet grinding was carried out to K4 Nb6 O17 (1.0–10 mm) powder using a ballmilling method. Consequently, the particle size became small (0.1–2.0 mm), and the photocatalytic activity was enhanced.16 Therefore, the direct preparation of uniform fine particles of photocatalysts is well expected to increase the photocatalytic activity. The preparation of these layered compounds by utilizing any sol-gel techniques has not yet been reported. Herein, a layered perovskite type oxide, K2 La2 Ti3 O10 , was synthesized by the polymerized complex (PC) method based on polyesterification of ethylene glycol a)

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J. Mater. Res., Vol. 13, No. 4, Apr 1998

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and citric acid,17,18 and its photocatalytic activity is compared with that prepared by the conventional solid state reaction. II. EXPERIMENTAL

K2 La2 Ti3 O10 powders were prepared by the PC method as follows. Titanium tetraisopropoxide was first dissolved in