Enhancement of photocatalytic activity of CuO-Cu2O heterostructures through the controlled content of Cu2O

A heterostructure photocatalyst of CuOCu2O was prepared by a chemical-thermal oxidation process. The content of Cu2O in the nanocomposite can simply be controlled by the chemical oxidation time during the synthesis process. The structure, microstructure and valence state of synthesized samples were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The higher content of Cu2O reduced the particle size and agglomeration level. It was found that the particle size was 60 nm. The band gap energies, calculated by diffuse reflectance spectroscopy (DRS), change from 1.65 to 1.90 eV by the higher content of Cu2O. Also, photoluminescence spectroscopy (PL) indicated a decrease in the electron-hole recombination rate by the increase in the content of Cu2O. The impact of the content of Cu2O on the photocatalytic activity and mechanism was investigated by the methylene blue (MB) and methyl orange (MO) degradation under the visible light irradiation. The efficiency of the degradation of MB by the CuOCu2O photocatalyst was higher than that of MO and increased by the higher content of Cu2O. To explain the contribution of different reactive species during photocatalysis, the effect of active group scavengers on degradation was investigated. The results indicated that hydroxyl radicals and holes were more effective reactive species in the photodegradation of MB and MO respectively. Also, the reason for the enhanced photocatalytic degradation by the CuOCu2O nanopowder with the higher content of Cu2O was explained by the proposed photocatalytic mechanism.