The mechanism of photocatalytic CO2 reduction by graphene-supported Cu2O probed by sacrificial electron donors

Abstract

Cu₂O nanoparticles of 5 nm average size have been adsorbed (1.74 wt% loading) on defective graphene (Cu₂O/G) previously obtained by the pyrolysis of alginic acid sodium salt. The Cu₂O crystal phase was determined by XRD. XPS shows that the external layers of the Cu₂O nanoparticles are constituted mainly of Cu⁺ although a certain percentage of Cu^II+ was also present. Cu₂O/G is a photocatalyst for the CO₂ reduction to methane in the presence of sacrificial agents, and the rate of CH₄ production depends on the oxidation potential of the electron donor. This relationship supports a mechanism involving photoinduced charge separation with the generation of electrons and holes. The highest CH₄ formation rate upon UV-Vis irradiation of Cu₂O/G with a 300 W Xe lamp was achieved for dimethylaniline reaching 326 μmol CH₄ per g per h. The spectral response of the Cu₂O photocatalyst shows, however, that the response of the photocatalyst is mainly due to UV irradiation, indicating that light absorption at the low Cu₂O loading on the Cu₂O/G photocatalyst occurs mainly on the graphene component.