Photocatalyzed Production of Hydrogen and Iodine from Aqueous Solutions of Iodide Using Platinum-Loaded TiO2 Powder

Hydrogen evolution and oxidation of iodide on photoirradiated Pt-loaded TiO2 powder were studied in the deaerated solutions containing iodide ions. These photocatalytic reactions have been considered to be difficult because the reaction is endothermic and reversible. However, we found that under some experimental conditions the reactions proceeded until the concentration of I3− ions reached a limiting level. The initial rate of the reactions and the limiting concentration of I3− ions in solution were enhanced as the pH of the solution decreased. In order to elucidate the pH dependence, the anodic current due to the oxidation of iodide ions on TiO2 film electrodes and the adsorptivity of iodide ions on TiO2 powder were measured. The results showed that the enhanced reactivity at low pH is due to the increased adsorptivity of iodide ions on TiO2. It was also found that the electric contact between platinum and TiO2 is important to make the reactions go forward.