Significant influence of solvent on hydrogen production from aqueous I3−/I− redox solution using dye-sensitized Pt/TiO2 photocatalyst under visible light irradiation

H2 production from a water–acetonitrile mixed solution containing iodide electron donor was investigated over dye-sensitized Pt/TiO2 photocatalysts under visible light irradiation. Merocyanine and coumarin dyes were utilized as photosensitizers. The rates of H2 evolution, which decreased with the increasing water amount in the mixed solutions, were ascribed to the decrease in energy gap between the redox potential of I3−/I− and the HOMO level of the dye. The observed high rate of H2 production even in an aqueous solution over a coumarin-sensitized Pt/TiO2 photocatalyst shows that the dye has a sufficiently positive HOMO level relative to the oxidation potential of I−.