Dye-sensitized photocatalysts for efficient hydrogen production from aqueous I− solution under visible light irradiation

H2 production from a water–acetonitrile (AN) mixed solution containing iodide electron donor was investigated over dye-sensitized Pt/TiO2 photocatalysts under visible light irradiation. It was found that H2 production with good quantum efficiency (∼2.5%) took place using merocyanine and coumarin dye-sensitized Pt/TiO2 photocatalysts, respectively, and an I− electron donor in a water–acetonitrile mixture (water, 5% by volume). The rates of H2 evolution were decreased with the increase of the water amount in the mixed solution because of the decrease in energy gap between the redox potential of I3−/I− and the HOMO level of the dye. H2 evolution was also decreased with the accumulation of produced I3− from I−. However, we have also found that it is possible to prevent the backward reaction, reduction of I3− to I− on Pt metal by using the internally platinized semiconductor K4Nb6O17 instead of Pt/TiO2 in water–AN mixed solution.