**Acknowledgements**

of TiO2 in order to generate charge carriers. This surface-to-bulk interfacial electron transfer enhances charge separation (Effect 3). The surface modification permits the electron transfer from the CB of TiO2 to shallow vacant surface oxocomplex levels, which distribute around ca.

**Sheme 3.** Surface modification effects of the Fe oxocomplex on the TiO2-photocatalyzed decomposition of organic pol‐

in the Cu2+-grafted TiO2 system under visible-light irradiation [42]. In this cathodic process, the electrons efficiently reduce adsorbed O2 with the aid of the electrocatalytic activity of the surface-adsorbed oxocomplex (Effect 4). This effect should also contribute to the increase in the UV-light activity. In the anodic process, the holes generated in the VB could take part in the oxidation process without diffusion (Effect 5) [15]. Consequently, Fe2O3/TiO2 as well as NiO/TiO2 and Co2O3/TiO2 satisfy the three requirements of the "solar environmental catalyst."

The surface of TiO2 can be modified by oxocomplexes of the first transition metals (MOCs/ TiO2) with the loading amount precisely controlled by using the CCC technique. Among the MOCs/TiO2, Fe2O3-, Co2O3- and NiO-surface-modified TiO2 possess unique physicochemical properties such as strong visible-light absorption and the excellent reduction ability of O2. Spectroscopic experiments and first-principles DFT simulation have revealed that the surface modification with the MOCs raises the VB maximum of TiO2 due to the formation of plural metal–O–Ti interfacial bonds. Surface-to-bulk and/or bulk-to-surface interfacial electron transfer induced by visible-light absorption enhances charge separation. This novel coupling system consisting of MOCs and TiO2 would be promising as the "solar environmental

radicals was confirmed by chemiluminescence photometry

−

lutants. The levels around −0.2 V show the vacant Fe oxocomplex.

370 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

−0.2 V [22]. The formation of O2

catalyst."

**7. Conclusions and future prospect**

A series of studies on metal oxocomplex–surface-modified TiO2 have been performed in collaboration with Dr. Michael Nolan and Dr. Anna Iwaszuk (Tyndall National Institute, University College Cork). The authors are sincerely grateful for their very useful DFT simu‐ lations. Also, the authors acknowledge Dr. M. Fujishima (Kinki University) for a helpful discussion, and T. Hattori, S. Okuoka, and Y. Sumida (Nippon Shokubai Co.) for EXAFS measurements and a valuable discussion. Ishihara Sangyo Co. gifted us with ST-01, and K. Fujiwara aided us in the collection and arrangement of the materials. H.T. acknowledges the support from the Ministry of Education, Science, Sport, and Culture, Japan, through a Grantin-Aid for Scientific Research (C) No. 24550239, No. 15K05654, MEXT-Supported Program for the Strategic Research Foundation at Private Universities, and Nippon Sheet Glass Foundation for Materials Science and Engineering, and by Sumitomo Foundation.
