Visible-Light-Induced Photocatalytic Hydrogen Production over Binuclear RuII-Bipyridyl Dye-Sensitized TiO2 without Noble Metal Loading

Highly efficient, visible light induced photocatalytic H2 production was achieved over a TiO2 system sensitized by binuclear RuII bipyridyl (bpy) complex [Ru2(bpy)4(BL)](ClO4)2 (BL=bridging ligand) without Pt loading, which is almost unaffected by pH in aqueous solution in the wide range from pH 5.00 to 10.50, although the dye molecules can only be loosely attached to TiO2 due to the absence of terminal carboxyl groups. The photocatalyst shows remarkable long-term stability and reproducibility of H2 evolution even after exchanging the aqueous triethanolamine solution. The amount of H2 evolved over 100 mg of photocatalyst in 27 h of irradiation corresponds to a turnover number of about 75?340, and the apparent quantum yields are estimated to be 16.8 and 7.3?% under 420 and 475 nm monochromatic light irradiation, respectively. A comparative study shows that the loosely attached dye [Ru2(bpy)4(BL)](ClO4)2 has higher photosensitization efficiency than tightly linked dyes with terminal carboxyl groups, such as [Ru2(dcbpy)4(BL)](ClO4)2 and N719. It can be rationalized by their different coordination, physicochemical, electron-injection, and back-transfer properties.