Synthesis of hierarchical Cd-Ni-MOF micro/nanostructures and derived Cd-Ni-MOF/CdS/NiS hybrid photocatalysts for efficient photocatalytic hydrogen evolution

Abstract

Hierarchical micro/nanostructures assembled from nanorods and nanosheets have become promising candidates for photocatalysis. In this work, a series of hierarchical Cd-Ni-MOF micro/nanostructures, assembled from nanosheets and nanorods, were fabricated via a two-step solvothermal process involving the partial replacement of Ni²⁺ with Cd²⁺ in the Ni-MOF-74 structure. Different morphologies were obtained by considering different volume ratios of DMF and ethanol as the solvent during synthesis. Hierarchical Cd-Ni-MOF-T/CdS/NiS hybrid micro/nanostructures were synthesized by Ni²⁺ and Cd²⁺ exchange of Cd-Ni-MOFs with S²⁻. The as-prepared samples, which were composed of thin nanosheets alone, exhibited the best photocatalytic H₂ evolution rate of about 40.08 mmol g⁻¹ h⁻¹. The p–n junction between CdS and NiS was found to be beneficial for the migration of photogenerated electrons from the conduction band (CB) of NiS to the CB of CdS. The heterojunction between CdS and Cd-Ni-MOF-T further promoted the transfer of an electron from the CB of CdS to the CB of Cd-Ni-MOF-T. Thus, this study demonstrated that hierarchical Cd-Ni-MOF-T/CdS/NiS architectures have a large specific surface area, leading to significantly improved photocatalytic activity.