Degradation of carboxylic acids on Y2O3 surface under UV light. Synergism by semiconductors

Under UV light formic, oxalic, acetic and citric acids undergo degradation on the surface of Y2O3, an insulator. The oxidation of oxalic acid displays first-order kinetics with a linear dependence on light intensity. The photonic efficiency is lower with UV-A light than with UV-C light. While particulate TiO2, ZnO, CuO, Bi2O3 and Nb2O5 individually photocatalyze the oxidation, each semiconductor when present along with Y2O3 shows synergism, indicating interparticle electron-jump from oxalic acid-adsorbed Y2O3 to the band gap-excited semiconductor on collision. The ease of photodegradation of the acids on Y2O3 is as follows: formic>oxalic>acetic>citric.