Photocatalytic oxidation of oxalic acid enhanced by silver and copper deposition on a TiO2 surface

Photooxidation of oxalic acid over a TiO2 surface in the presence of Ag+ and Cu2+ ions was studied. Reduction of metal ions and oxidation of oxalic acid were followed under irradiation of aqueous suspensions of pH 2.5-3.5. It has been demonstrated that, after the completion of silver deposition, the small metal particles on the TiO2 surface enhance the efficiency of the semiconductor by a factor of 5 for the photooxidation of oxalic acid. The photoreduction of Cu(II) also occurs. Although a small fraction of Cu(II) is reduced and deposited on TiO2 under photolysis in the presence of oxygen, the photooxidation of oxalic acid is more effective in this system than has been found for Ag-deposited TiO2. The quantum yields for photooxidation of oxalic acid have been determined at various wavelength between 350 and 420 nm. These data demonstrate that the deposition of either Ag or Cu on the TiO2 surface results in a shift of 1,200 cm(-1) in the band gap to lower energies and a considerable increase in the efficiency of photooxidation owing to the efficient separation of photogenerated holes and electrons.