Zn(II)-doping enhanced photocatalytic activity of Cu₂O nanocrystals

Zn(II)-doped octahedral and hexahedral Cu₂O nanocrystals were synthesized with a green and gentle process. It was found that Zn-doping both tuned the Cu₂O polyhedrons into quasi-spheres and decreased their sizes. The reduced lattice parameter as demonstrated in X-ray diffraction patterns (XRD), the increased binding energy of Cu(I) in X-ray photoelectron spectrum (XPS) and the uniform elemental distribution as exhibited in energy dispersive spectroscopy (EDS) mapping image provided solid evidence for the successful doping of Zn(II) in Cu₂O nanocrystals. Zn(II) was verified to be surface enrichment, which might protect Cu₂O from oxidation. Enhanced photocatalytic activity was observed with the degradation of methyl orange (MO) and methylene blue (MB) as the model reactions when the Zn-doping concentration was lower than 1%. UV-visible absorption spectra of the Zn-doped products showed red-shift in comparison with the pure Cu₂O counterparts. The decreased band gap and the retarded oxidation were believed to be responsible for the improved catalytic activity. This method provides a new idea for the controlled synthesis of other doping materials and the study of the related photocatalytic activity.