Visible-Light-Induced Electron Transport from Small to Large Nanoparticles in Bimodal Gold Nanoparticle-Loaded Titanium(IV) Oxide

A key to realizing the sustainable society is to develop highly active photocatalysts for selective organic synthesis effectively using sunlight as the energy source. Recently, metal-oxide-supported gold nanoparticles (NPs) have emerged as a new type of visible-light photocatalysts driven by the excitation of localized surface plasmon resonance of Au NPs. Here we show that visible-light irradiation (lambda > 430 nm) of TiO2-supported Au NPs with a bimodal size distribution (BM-Au/TiO2) gives rise to the long-range (> 40 nm) electron transport from about 14 small (ca. 2 nm) Au NPs to one large (ca. 9 nm) Au NP through the conduction band of TiO2. As a result of the enhancement of charge separation, BM-Au/TiO2 exhibits a high level of visible-light activity for the one-step synthesis of azobenzenes from nitrobenzenes at 25 degrees C with a yield greater than 95% and a selectivity greater than 99%, whereas unimodal Au/TiO2 (UM-Au/TiO2) is photocatalytically inactive.