Zn-Doped CdS Nanoarchitectures Prepared by Hydrothermal Synthesis: Mechanism for Enhanced Photocatalytic Activity and Stability under Visible Light

Zn-doped CdS nanoarchitectures with different Zn content are synthesized by a simple hydrothermal method with water as the only solvent. The prepared samples are characterized by X-ray powder diffraction, scanning electron microscopy, UV-vis diffuse reflectance spectra, Brunauer-Emmett-Teller measurement, and X-ray photoelectron spectroscopy, while the photocatalytic activities are tested by photocatalytic degradation of rhodamine-B under visible-light irradiation. The results show that CdS with small amount of Zn doping can lead to an enhanced photocatalytic activity. Zn-doped CdS sample derived at 160 degrees C for 12 h with the molar ratio of Zn/Cd = 1:10 exhibits the best photocatalytic activity, which is much higher than that of pure CdS. Moreover, there is almost no loss of photocatalytic activity after four cycles of repeated experiments. So, Zn2+ doping indeed improves the photocatalytic activity and stability of CdS. Theoretical calculation indicates that Zn doping into a CdS crystal lattice can result in the shift of the valence band of CdS to a positive direction. It may lead to its higher oxidative ability than pure CdS, which is important for organic pollutant degradation under visible-light irradiation. Furthermore, the low formation energy for Zn-doped CdS systems demonstrates that the stability of CdS with Zn2+ doping can be improved. Experimentally and theoretically, this study will be useful for the improvement of photocatalytic activity and stability of CdS through the method of metal ion doping.