Synthesis and visible light photocatalytic activities of Au/Cu₂O heterogeneous nanospheres

Au/Cu₂O heterogeneous spheres (HGS) were prepared by in situ reduction of preadsorbed AuCl^-₄ on the surface of Cu₂O mesoporous spheres (MPS) linked by L-cysteine. The resulting products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), and N₂ physical adsorption. The photocatalytic activity of the samples was evaluated by photocatalytic degradation of methylene blue (MB) under visible light (λ >400 nm) irradiation. The experimental results revealed that the Cu₂O MPS kept their mesoporous structure after loading with Au, and small Au nanoparticles (NPs) with a diameter of ~4 nm were identified on the surface of the MPSs. N₂ physical adsorption analysis showed that the pore size distributions of Cu₂O MPSs were unchanged after loading with Au NPs. Using ethanol as a solvent retarded the redox reaction between AuCl^-₄ and Cu₂O, avoiding damage to the mesoporous structures. The Au/Cu₂O HGSs exhibited higher visible-light photocatalytic activity for the degradation of methylene blue than the pure Cu2O MPSs. The enhanced photocatalytic efficiency of the Au/Cu₂O HGSs was attributed to rapid charge transfer from Cu₂O to the loaded Au NPs as well as the surface plasmon resonance of Au NPs.