Highly Active Subnanometer Au Particles Supported on TiO2 for Photocatalytic Hydrogen Evolution from a Well-Defined Organogold Precursor, [Au5(mesityl)5]

A highly efficient H-2 evolution photocatalyst based on TiO2 supported subnanometer Au particles was developed on the basis of the reaction of a gold(I) molecular precursor [Au(5)Mes(5)] (Mes = 2,4,6-trimethylphenyl), with titanium dioxide partially dehydroxylated at 120 degrees C. IR, UV vis, elemental analysis, XANES, and STEM-EDX show that the deposition of [Au(5)Mes(5)] onto TiO2 leads to the formation of both subnanometer Au particles and chemisorbed [Au(5)Mes(5)]. The remaining organic ligands are removed via a mild treatment under H-2, yielding subnanometer gold(0) particles. A range of Au loadings (0.3, 0.9, 2.4 wt %) with similar particle sizes (<1 nm) on TiO2 are obtained and tested in methanol-assisted photocatalytic hydrogen production under UV light. These catalysts display significantly higher activity than a commercial reference Au-TiO2 catalyst. The presence of chemisorbed [Au(5)Mes(5)] in the as-synthesized catalyst further improved activity, albeit at the expense of stability. This work demonstrates a simple synthetic route to obtain subnanometer Au particles on TiO2 that display exceptional activity in photocatalysis.