Photoinduced Reaction at TiO₂ Particles. Photodeposition from NiII Solutions with Oxalate

In a photoinduced reaction, an intermediate produced by the reaction of a reductant R with photogenerated holes can promote a reduction reaction that is not observed in the absence of R. We illustrate this scheme by considering the reduction of NiII at TiO2. In this case NiII, which is not deposited on illuminated TiO2, can be reduced by the intermediate CO2•- produced from the anodic oxidation of oxalate ion (C2O42-) at irradiated TiO2 in water. Irradiation of an aqueous NiII solution containing 10 μg Ni/mL in the presence of TiO2 particles led to 85% removal of the Ni from the solution. The mechanism of the reaction was probed by measurement of current-doubling effects for oxalate solutions at a single-crystal TiO2 electrode.