Regulating the surface state of ZnIn2S4 by gamma-ray irradiation for enhanced photocatalytic hydrogen evolution

Abstract

Surface vacancies have been demonstrated to be active sites in the photocatalytic hydrogen-evolution reaction (HER) over sulfides and oxides. In this work, the surface S vacancies were regulated by high-energy γ-ray radiation over ZnIn₂S₄. It was found that γ-ray irradiation had a strong effect on changing the electronic structure, and ZnIn₂S₄ had a variable band gap under different radiation doses. With the dose of 40 kGy, the band gap of ZnIn₂S₄ was reduced from 2.11 to 2.01 eV. The H₂-generation rate under visible light could be as high as 154.1 μmol h⁻¹ over 40 kGy γ-ray-irradiated ZnIn₂S₄, which was approximately 11.5 times higher than that over the original ZnIn₂S₄. Furthermore, the ESR, XPS, and fluorescence spectroscopy provided evidence of γ-ray radiation-introduced surface S vacancies on the Zn side. DFT calculations demonstrated that the surface S vacancies accelerated H₂O adsorption and H₂ desorption. Nevertheless, a higher irradiation energy (>40 kGy) may create more bulk vacancies, resulting in a lower H₂-evolution activity. Therefore, γ-ray irradiation is beneficial to regulating the surface S vacancies on ZnIn₂S₄, thereby improving the photocatalytic H₂-evolution efficiency. This work provides a detailed understanding of γ-ray radiation-induced surface vacancies and a reasonable inspiration to regulate the surface defects of photocatalysts with efficient activity.