Highly Active Supported Plasmonic Photocatalyst Consisting of Gold Nanoparticle-Loaded Mesoporous Titanium(IV) Oxide Overlayer and Conducting Substrate

Abstract

We prepared mesoporous films consisting of gold nanoparticle-loaded titanium dioxide nanoparticles on various conducting substrates including FTO, ITO, Ti, Au, and Pt (Au/mp-TiO2/conducting substrate), and a glass plate for comparison. Electrochemical characterization of Au/mp-TiO2/FTO substrate clarified that the mesoporous structure of the Au/TiO2 overlayer permits the permeation of solution into the mesopores to reach the FTO surface. The visible-light activity (λ > 430 nm) of the immobilized “plasmonic photocatalysts” was evaluated for the oxidations of benzylamine and cinnamyl alcohol. The visible-light activity strongly depended on the kind of the substrates. Visible-light irradiation of Au/mp-TiO2/FTO in an aqueous solution of benzylamine selectively produced benzaldehyde with ∼100% yield at 16 h, while the yields for the Au/mp-TiO2/glass and Au/TiO2 particle systems were ∼75% under the same conditions. In the selective oxidation of cinnamyl alcohol to cinnamaldehyde, the Au/mp-TiO2/conducting substrate photocatalysts using Ti, Au, and Pt as the substrate showed significantly higher activities than even Au/TiO2 particles. By the technique for labeling and visualizing the reduction sites (J. Phys. Chem. B 2000, 104, 4585), this remarkable substrate effect was shown to originate from the long-range charge separation by the successive interfacial electron transfer from Au nanoparticle to the substrate through TiO2. A good positive correlation was found between the visible-light activity of Au/mp-TiO2/conducting substrate and the electrocatalytic activity of the conducting substrate for O2 reduction.