Design of All-Inorganic Molecular-Based Photocatalysts Sensitive to Visible Light:  Ti(IV)−O−Ce(III) Bimetallic Assemblies on Mesoporous Silica

The first photocatalysis operated by the visible-light induced metal-to-metal charge transfer (MMCT) has been demonstrated for the Ti(IV)/Ce(III) bimetallic assemblies synthesized on the pore of mesoporous silica. The Ce LIII-edge XANES measurements combined with 18O-isotopic labeling as well as photoelectrochemical experiments proved the ability of Ti(IV)/Ce(III) assemblies to drive the site-specific photocatalytic reaction under visible-light irradiation. Photocatalytic experiments using the oxidative decomposition of 2-propanol showed that the quantum efficiency for Ti(IV)/Ce(III) bimetallic photocatalysts was remarkably higher than that for the one of the most active visible-light sensitive photocatalysts, nitrogen-doped TiO2. It was also found that the grafting of Ce(III) ions onto nanocrystalline TiO2 particles led to the appearance of intense MMCT band in the visible-light regions, thus verifying it as the generally applicable strategy to obtain visible-light photocatalysts. To date, the grafting of metal cations on the pore of mesoporous silica has been established for about one-fourth of the elements in the periodic table. Therefore, the abilities of hetero-bimetallic assemblies to drive photocatalysis with a high quantum efficiency and their high flexibility in metal combination provide an opportunity to design and fabricate the wide variety of molecular-based inorganic photocatalysts according to the needs from the target reactions as well as their operation environments.