Photoassisted Platinum Deposition on TiO2 Powder Using Various Platinum Complexes

Article abstract of DOI:10.1021/j100280a114

The photocatalytic deposition of metallic platinum has been carried out with powder titania in aqueous suspension containing different complex solutions (chloroplatinic acid, sodium chloroplatinate, hexahydroxyplatinic acid, and platinum-dinitro-diammine).The deposition rate was found identical for the three first complexes and much more lower for the last one which is not ionic.In all cases the removal of the Pt ions from the solutions was achieved to the detection limit (1 ppm).Analyses of the solid, liquid, and gas phases indicated that the reduction of a (Ptⁿ⁺) complex ion induced, as expected, the release of n protons in the solution, whereas oxygen evolution from water oxidation was completely blurred by an initial photodesorption of preexisting ionosorbed oxygen species, followed by the dissociative chemisorption of O2 on the Pt crystallites formed in the process.A mechanism is proposed from the effects of various parameters (initial concentration, light flux, temperature).An initial quantum yield of about 0.05 was calculated.Transmission electron microscopy showed that platinum deposits initially as small crystallites of 1 nm diameter distributed on all the particles of titania.For higher loadings and longer illumination times, large agglomerates form; as a result, most of semiconductor surface remains accessible to the photons so that the activity for the deposition does not decline.Pd, Ag, Rh, Au, and Ir have also been deposited on TiO2 whereas Ni and Cu were not.Preliminary experiments indicated that ZnO, Nb2O5, and ThO2, for instance, can be used instead of TiO2.