The Effect of Methanol on the Photodeposition of Pt Nanoparticles on Tungsten Oxide

Formation of platinum nanoparticles on tungsten oxide by photodeposition from acidic [PtCl6](2-) solutions in the absence or presence of methanol is studied in detail. Without methanol, [PtCl6](2-)-ions adsorbed on the WO3 surface are converted to highly dispersed PtO/Pt(OH)(2) particles upon illumination, the maximum achievable amount being limited to 10-30% of [PtCl6](2-) present in solution. Inclusion of methanol not only promotes adsorption of [PtCl6](2-) ions, but upon illumination results in a deposited Pt quantity close to 100% of [PtCl6](2-). The obtained Pt particles are in the metallic state, large, and often clustered. The limited loading and presence of PtO/Pt(OH)(2) in the absence of methanol is explained by reduction of WO3-surface sites, accompanied by water oxidation catalyzed by PtO/Pt(OH)(2) deposits. The extensive reduction of Pt in methanol solutions is likely induced by methoxy-radicals, oxidatively formed by reaction of methanol with photogenerated holes. This study provides guidelines for optimization of synthesis procedures of Pt/WO3 (photo)catalysts.