Three-dimensional flower-like ZnIn2S4/NiO/ZIF-67 hierarchical spheres for enhanced visible-light photocatalytic hydrogen evolution

Abstract

Photocatalysis has been recognized as a promising strategy to produce H₂ energy. In this work, three-dimensional (3D) flower-like ZnIn₂S₄/NiO/ZIF-67 hierarchical spheres were synthesized successfully. The as-prepared 3D ZnIn₂S₄/NiO/ZIF-67 catalyst exhibits a high photocatalytic hydrogen production performance of 13 975 μmol g⁻¹ h⁻¹. This study found that NiO/ZIF-67 can improve the visible-light absorption capacity of ZnIn₂S₄ (ZIS) significantly and narrow its band gap from 2.33 to 2.07 eV. Meanwhile, the ultrathin ZIS nanosheets were uniformly grown on the surface of NiO/ZIF-67, which can avoid agglomeration of ZIS. After loading NiO/ZIF-67, the specific surface area of the catalyst increased from 133.47 to 159.29 m² g⁻¹, exposing rich active sites for photocatalytic redox reactions. Through various tests, it was observed that the enhanced H₂ production was due to the high charge carrier generation and separation. Density functional theory (DFT) calculations confirmed that electrons could transfer from NiO/ZIF-67 to ZIS, splitting the adsorbed water. Accordingly, the H–O bond length of water on ZnIn₂S₄/NiO/ZIF-67 increased from 0.975 to 0.989 Å. Meanwhile, a possible mechanism for photocatalytic hydrogen evolution was proposed according to the results.