Oxalic acid is photooxidized on Pr6O11 surface under UV-A light and the reaction follows first-order kinetics with a linear dependence on the photon flux. The photonic efficiency is higher with UV-C light than with UV-A light. While TiO2, ZnO, CuO, Bi2O3, and Nb2O6 individually photocatalyze the oxidation, each semiconductor, when present along with Pr6O11 shows enhanced oxidation indicating interparticle hole-jump from the band gap-excited semiconductor to oxalic acid-adsorbed on Pr6O11. The photonic efficiency of the oxidation on Pr6O11 surface is of the order: formic acid > oxalic acid > acetic acid: citric acid is unsusceptible to oxidation. (C) 2009 Elsevier B.V. All rights reserved.