Heterogeneous photocatalytic reactions comparing TiO2 and Pt/TiO2

Two commercial samples, namely Degussa P-25 and Sachtleben Hombikat UV 100, and platinized modifications of these samples have been tested comparatively as photocatalysts for EDTA oxidation and for Cr(VI) reduction in the absence and in the presence of EDTA. Platinized photocatalysts were prepared by photoimpregnation of H(2)PtCl(6) on TiO(2) by prolonged irradiation in the presence of methanol. Only slight differences in efficiency were found between both pure commercial forms, except for the Cr(VI) reduction in the presence of EDTA, where Hombikat UV 100 samples were more active. Platinized Hombikat UV 100 was found to be less active for Cr(VI) reduction in water. The concentration of dissolved molecular oxygen was crucial for EDTA oxidation and had no influence on Cr(VI) reduction. From kinetic profiles, initial photonic efficiencies () and conversion degrees have been calculated. Platinization did not improve Cr(VI) reduction but increased the initial photonic efficiency for EDTA oxidation. However, after prolonged irradiation, the conversion of EDTA was lower employing platinized samples instead of pure samples. The effect of platinum on titania was analyzed on the basis of proposed mechanisms. (C) 2002 Published by Elsevier Science B.V.