Photocatalytic reactions involving radical chain reactions using microelectrodes

The mechanism of photocatalytic decomposition of ethanol in aqueous solution was studied using a microelectrode technique. We employed a partially Pd-covered TiO2 film as a model for the metal-deposited photocatalyst. We observed concentration changes of dissolved oxygen and H2O2 caused by the photocatalytic reaction in the absence and presence of ethanol separately above the bare TiO2 and Pd-covered surfaces. It is clearly shown that dissolved oxygen is consumed even on oxidation sites of the photocatalyst in the presence of ethanol, producing H2O2. On the basis of these results, we conclude that radical chain reactions proceed at oxidation sites (i.e., bare TiO2) but not at reduction sites (i.e., Pd-covered surface) on the photocatalyst.