Effect of Water/Acetonitrile Ratio on Dye-Sensitized Photocatalytic $H2$ Evolution under Visible Light Irradiation

$H2$ production in a water-acetonitrile solution containing iodide as an electron donor was investigated over dye-sensitized $Pt∕TiO2$ photocatalysts under visible light irradiation, as a potential water-splitting system based on an iodide redox mediator. The rates of $H2$ evolution decreased with increasing proportion of water in the solutions, because of a decrease in the energy gap between the redox potential of $I3−∕I−$ and the highest occupied molecular orbital levels of the dyes, which decreases the efficiency of electron transfer from $I−$ to dye.