A bi-overlayer type plasmonic photocatalyst consisting of mesoporous Au/TiO2 and CuO/SnO2 films separately coated on FTO

Abstract

The principal purpose of this study is to present a new design for preparing highly active immobilized gold nanoparticle-based plasmonic photocatalysts. Gold nanoparticles were loaded on rutile TiO₂ particles with a mean size of 80 nm (Au/TiO₂) by the deposition precipitation method. The surface of SnO₂ particles with a mean size of 100 nm was modified by copper(II) oxide clusters (CuO/SnO₂) with the loading amount (Γ/Cu ions nm⁻²) precisely controlled by the chemisorption–calcination cycle technique. Two mesoporous overlayers of Au/TiO₂ and CuO/SnO₂ were coated side by side on glass substrates with a fluorine-doped tin oxide film (FTO) using the doctor blade method (Au/mp-TiO₂|FTO|CuO/mp-SnO₂). As test reactions for assessing the visible-light activity, we carried out gas-phase decomposition of acetaldehyde and liquid-phase oxidation of alcohol. In each reaction, this bi-overlayer type catalyst shows a high level of visible-light activity much exceeding those of Au/TiO₂ particles and a Au/mp-TiO₂|FTO mono-overlayer type catalyst [J. Phys. Chem. C, 2014, 118, 26887]. To confirm the origin of the striking visible-light activity, we studied the electrocatalytic activity of CuO/mp-SnO₂|FTO electrodes for the oxygen reduction reaction (ORR). Both the visible-light activity of Au/mp-TiO₂|FTO|CuO/mp-SnO₂ and the electrocatalytic activity of CuO/mp-SnO₂|FTO for ORR strongly depend on the Γ value. A good positive correlation has been found between the visible-light activities and the electrocatalytic activity for ORR. The striking activity of the present bi-overlayer type catalyst can be attributed to the efficient and long-range charge separation by the vectorial electron transport (Au(oxidation sites) → TiO₂ → FTO, SnO₂ → CuO(reduction sites)) and the excellent electrocatalytic activity of the CuO clusters.