Influence of different ruthenium(II) bipyridyl complex on the photocatalytic H2 evolution over TiO2 nanoparticles with mesostructures

H2 production over dye-sensitized Pt/TiO2 nanoparticles with mesostructures (m-TiO2) under visible light (λ > 420 nm) was investigated by using methanol as electron donors. Experimental results indicate that three types of ruthenium(II) bipyridyl complex dyes (one binuclear Ru, two mononuclear Ru), which can be attached to Pt/m-TiO2 with different linkage modes, show different photosensitization effects due to their different coordination circumstances and physicochemical properties. The dye tightly linked with m-TiO2 has better durability but the lowest H2 evolution efficiency, whereas the loosely attached dyes possess higher H2 evolution efficiency and preferable durability. It seems that the dynamic equilibrium between the linkage of the ground state dye with TiO2 and the divorce of the oxidization state dye from the surfaces plays a crucial role in the photochemical behavior during the photocatalyst sensitization process. It is helpful to improve the H2 evolution efficiency by enhancing the electron injection and hindering the backward transfer. The binuclear Ru(II) dye shows a better photosensitization in comparison with mononuclear Ru(II) dyes due to its large molecular area, conjugation system, and “antenna effect”, which, in turn, improve the visible light harvesting and electron transfer between the dye molecules and TiO2.