Synthesis, characterization and photocatalytic activity of Cu-doped Zn/ZnO photocatalyst with carbon modification

Abstract

Herein, we report the preparation of Cu-doped Zn/ZnO composites with carbon modification via a simple replacement–hydrothermal method using Zn powder and CuSO₄·5H₂O as raw materials. The as-synthesized composites were characterized by powder X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). The results showed that Cu doping promotes crystal growth of ZnO, inhibits phase transfer of metallic Zn to ZnO, enhances the optical absorption in the visible region and reduces the recombination of photogenerated electrons and holes. Interestingly, CO₂ dissolved in solution was converted to carbon adhered onto the composite surface (supported by the XPS data). The abundant carbon species present on the composite surface is favorable for surface chemical reactions because it can trap or adsorb reactants which facilitate the transfer of reactants to active sites. The photocatalytic efficiency of the as-synthesized catalysts was evaluated by the degradation of anthraquinone dye (reactive brilliant blue KN-R) in solution under sunlight irradiation. The degradation results revealed that the Cu-doped Zn/ZnO composites have better photocatalytic activities than those of ZnO and Zn/ZnO. The enhancement of the photocatalytic activity of the composites can be attributed to the existence of Cu doping, the Zn/ZnO hetero-structure and covered carbon on the surface of the photocatalysts, which causes electrons to be easily excited from the valence band to the conduction band and efficient separation of electron–hole pairs, as well as quick surface reactions in doped ZnO. Furthermore, a possible growth mechanism of the Cu-doped Zn/ZnO composites with carbon modification was proposed.