Enhanced photocatalytic hydrogen evolution over Cu-doped ZnIn ₂S₄ under visible light irradiation

A series of Cu-doped ZnIn₂S₄ photocatalysts has been synthesized by a facile hydrothermal method, with the copper concentration varying from 0 wt% to 2.0 wt%. The physical and photophysical properties of these Cu-doped ZnIn₂S₄ photocatalysts were characterized by X-ray diffraction (XRD), photoluminescence spectroscopy (PL), scanning electron microscopy (SEM), and UV-visible diffuse reflectance spectroscopy (UV-vis). The diffuse reflectance and photoluminescence spectra of Cu-doped ZnIn₂S₄ shifted monotonically to longer wavelengths as the copper concentration increased from 0 wt% to 2.0 wt%, indicating that the optical properties of these photocatalysts greatly depended on the amount of Cu doped. Meanwhile, the layered structure of ZnIn₂S₄ would be destructed gradually by Cu doping. The photoactivity of ZnIn ₂S₄ was enhanced when Cu²⁺ was doped into the crystal structure. The highest photocatalytic activity was observed on Cu (0.5 wt%)-doped ZnIn₂S₄, with the rate of hydrogen evolution to be 151.5 μmol/h under visible light irradiation (λ > 430 nm). On the basis of the calculated energy band positions and optical properties, the effect of copper as a dopant on the photocatalytic activity of Cu-ZnIn ₂S₄ was studied.