Photocatalytic systems working under visible light have been studied extensively from the viewpoints of energy conversion and environmental accountability. Recently, it was discovered that substitutional doping with anion elements to semiconductor photocatalysts leads to extension of the photoactive region to visible light. However, the present achievements are not enough compared to the performance demanded by the practical application. The main obstacle toward this is the fact that design and control of properties of semiconductor photocatalysts is strictly limited in flexibility, since the doping needs to be made under highly reactive conditions. In the present work, we have shown the use of metal-to-metal charge transfer (MMCT) of Ti(IV)-O-Ce(III) bimetallic moieties as a new class of visible-light sensitive photocatalysts. 1
The advantage of hetero-bimetallic photocatalysts is their high flexibility to design and control the electronic properties of photoreaction centers. 2 The oxidation/reduction potential as well as absorption wavelength of photocatalysts can be readily controlled by selecting the proper combination of two metal ions according to their redox potential. Furthermore, such control can be realized without using organic ligands. The choice of metal combination of Ti(IV) and Ce(III), in this work, enabled to drive the photocatalytic reactions under the visible-light induced MMCT. Their activities for catalytic oxidation of organic compounds were found to be remarkably higher than those for one of the most active visible-light photocatalysts, nitrogen-doped TiO₂.

Reference
(1) R. Nakamura and K. Hashimoto et al. JACS, 2007, 129, 9596-9597
(2) W. Lin and H. Frei JACS, 2005, 127, 1610-1611