The influence of platinum (II) on TiO2 photocatalyzed dye decolourization by rutile, P25 and PC500

The effect of deposition of 0.38% Pt(II) on the UV photocatalyzed decolouration of Reactive Orange 16 (RO16) and Malachite Green (MG) is reported for rutile TiO2, for anatase PC500, and for the mainly anatase P25. The metal loading and oxidation state were those that previously [17], gave the largest enhancement (×37) of the UV photocatalyzed degradation of DCA, when Pt was deposited on rutile. For rutile, Pt(II) deposition enhanced the rate of UV decolouration (×20, for RO16, or ×8, for MG). For PC500, Pt(II) deposition on PC500 reduced the decolouration of RO16 and increased the UV photocatalyzed decolouration of MG by only ×1.2. On P25, Pt(II) significantly reduced the UV photocatalyzed decolouration of both dyes. Previously, [17], Pt(II) deposition on P25 enhanced DCA degradation by a factor of only 1.5. Complementary measurements showed that visible-light photocatalytic decolouration rates were small on all the catalysts. It was inferred that platinum influences the UV photocatalysis by facilitating the electron transfer to adsorbed oxygen, and that this facilitation is much more important for rutile than for anatase because formation of O2− is more difficult on Pt-free anatase than on Pt-free rutile.