Gold–Copper Nanoalloys Supported on TiO2 as Photocatalysts for CO2 Reduction by Water

Abstract

Commercial P25 modified by Au–Cu alloy nanoparticles as thin film exhibits, for CO₂ reduction by water under sun simulated light, a rate of methane production above 2000 μmol (g of photocatalyst)⁻¹ h^–1. Although evolution of hydrogen is observed and O₂ and ethane detected, the selectivity of conduction band electrons for methane formation is almost complete, about 97%. This photocatalytic behavior is completely different from that measured for Au/P25 (hydrogen evolution) and Cu/P25 (lower activity, but similar methane selectivity). Characterization by TEM, XPS, and UV–vis spectroscopy shows that Au and Cu are alloyed in the nanoparticles. FT-IR spectroscopy and chemical analysis have allowed one to detect on the photocatalyst surface the presence of CO₂^•–, Cu–CO, and elemental C. Accordingly, a mechanism in which the role of Au is to respond under visible light and Cu binds to CO and directs the reduction pathway is proposed.