Improving photocatalytic activity for hydrogen evolution over ZnIn ₂S₄ under visible-light: A case study of rare earth modification

A series of rare earth (RE) ions (La³⁺, Ce³⁺, Gd ³⁺, Er³⁺ or Y³⁺) modified ZnIn ₂S₄ 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 RE ₂O₃ and their modification can reduce ZnIn ₂S₄ crystallite size, inhibit ZnIn₂S ₄ grain growth, promote ZnIn₂S₄ crystallite self-organization into a micro-sphere flower-like morphology, increase ZnIn ₂S₄ 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.