LIU ET AL. VOL. 8 ’ NO. 7 ’ 7229–7238 ’ 2014 www.acsnano.org 7229 June 02, 2014 C 2014 American Chemical Society Enhanced Photoactivity with Nanocluster-Grafted Titanium Dioxide Photocatalysts Min Liu, ‡ Ryota Inde, † Masami Nishikawa, ^ Xiaoqing Qiu, ‡ Daiki Atarashi, † Etsuo Sakai, † Yoshio Nosaka, ^ Kazuhito Hashimoto, ‡,§, * and Masahiro Miyauchi †, ) , * † Department of Metallurgy and Ceramics Science, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan, ‡ Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan, § Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan, ^ Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1, Kamitomioka-machi, Nagaoka, Niigata 940-2188, Japan, and ) Japan Science and Technology Agency (JST), PRESTO, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan T he development of a safe, abundant and inexpensive photocatalyst is a significant consideration in solving the current energy and environmental issues. 1À6 Titanium dioxide (TiO 2 ) is one of the promising materials because of its non- toxic, resource abundant, chemically stable properties, and has therefore attracted a great deal of attention for the applications in water splitting, decomposition organic pollutants, solar cells and so on. 7À11 How- ever, TiO 2 has a wide band gap and can only be activated under ultraviolet (UV) light irradiation, which limits its practical applica- tions. To effectively utilize solar light and indoor light, the doping of TiO 2 with various transition metal cations and anions has been extensively investigated to extend its light absorption to visible light region. 12À20 Although most systems doped in this way can show visible light absorption, these sys- tems are still unsatisfactory for practical use, because their quantum efficiencies (QEs) under visible light are much lower than those under UV light. 21 This limit is mainly arisen from that the dopants generate impurity and/or vacancy levels in the band gap, which serve as the recombination centers for the photogenerated charge carriers. 12À21 As an alternative, Kisch et al. developed the photosensitization of TiO 2 by surface modification with platinum(IV) chloride. 22 The development of photocata- lyst by surface modification process is very attractive because the visible-light activity can be induced by the simple process without introduction of impurity or vacancy levels into crystal. TiO 2 grafted with some transition metal oxide nanoclusters, such as Fe(III) or Cu(II) nanoclusters, are also capable of serving as visible-light sensitive photo- catalysts. 23À27 When Fe(III) or Cu(II) nano- clusters were grafted onto the surface of TiO 2 , electrons in the valence band (VB) * Address correspondence to mmiyauchi@ceram.titech.ac.jp, hashimoto@light.t.u-tokyo.ac.jp. Received for review April 24, 2014 and accepted June 2, 2014. Published online 10.1021/nn502247x ABSTRACT Titanium dioxide (TiO 2 ), as an excellent photocatalyst, has been intensively investigated and widely used in environmental purification. However, the wide band gap of TiO 2 and rapid recombination of photogenerated charge carriers significantly limit its overall photocatalytic efficiency. Here, efficient visible-light-active photocatalysts were developed on the basis of TiO 2 modified with two ubiquitous nanoclusters. In this photocatalytic system, amorphous Ti(IV) oxide nanoclusters were demonstrated to act as hole-trapping centers on the surface of TiO 2 to efficiently oxidize organic contaminants, while amorphous Fe(III) or Cu(II) oxide nanoclusters mediate the reduction of oxygen molecules. Ti(IV) and Fe(III) nanoclusters-modified TiO 2 exhibited the highest quantum efficiency (QE = 92.2%) and reaction rate (0.69 μmol/h) for 2-propanol decomposition among previously reported photocatalysts, even under visible-light irradiation (420À530 nm). The desirable properties of efficient photocatalytic performance with high stability under visible light with safe and ubiquitous elements composition enable these catalysts feasible for large-scale practical applications. KEYWORDS: TiO 2 . nanocluster . visible light . photocatalysis . high quantum efficiency ARTICLE