Improving photocatalytic activity for hydrogen evolution over ZnIn2S4 under visible-light: A case study of rare earth modification

A series of rare earth (RE) ions (La3+, Ce3+, Gd3+, Er3+ or Y3+) modified ZnIn2S4 photocatalysts (RE-ZnIn2S4) were prepared using the hydrothermal method and characterized by various analysis techniques, such as UV–Vis diffusive reflectance spectroscopy, X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller surface analyzer, photoluminescence spectroscopy and X-ray photoelectron spectroscopy. The results indicated that the RE element exists as the oxide RE2O3 and their modification can reduce ZnIn2S4 crystallite size, inhibit ZnIn2S4 grain growth, promote ZnIn2S4 crystallite self-organization into a micro-sphere flower-like morphology, increase ZnIn2S4 surface area and total pore volume, and bring rich defects to ZnIn2S4. The photocatalytic activities of RE-ZnIn2S4 were evaluated based on photocatalytic hydrogen production from water under visible-light irradiation and the hydrogen production efficiency increased by 46%, 53%, 61%, 69%, and 106% after adding 2.0 wt% of Y, Gd, Er, Ce and La, respectively. The relationship between the photocatalytic activity of RE-ZnIn2S4 and the RE properties was discussed.