In situ meso-tetra (4-carboxyphenyl) porphyrin ligand substitution in Hf-MOF for enhanced catalytic activity and stability in photoredox reactions

Though there are numerous intrinsic merits of metal-organic frameworks (MOFs), low charge separation efficiency has imposed heavy restrictions on their photocatalytic application. Herein, in situ porphyrin ligand substitution, as a strategy for improving the charge separation efficiency and increasing the amounts of active sites, has been designed and realized in a Hf-biphenyl dicarboxylic acid (BPDC) MOF. Specifically, a size and geometry matched meso-tetra (4-carboxyphenyl) porphyrin (TCPP) ligand was selected and doped into Hf-BPDC MOF by forming coordinating bonds with Hf centers, forming dual-ligand Hf-BPDC-TCPP MOF. The resultant Hf-BPDC-TCPP MOF showed significantly improved activity and chemical stability in the photocatalytic H₂ generation (261 μmol·g⁻¹·h⁻¹) and tetracycline (TC) degradation reactions (95.8%), which was 48 and 1.47 folds higher than that of the Hf-BPDC MOF. Photophysical and electrochemical studies revealed that the introduction of porphyrin ligand could generate a stronger internal electric field for boosting the charge separation and transfer, increase the specific surface area for providing more active sites, and narrow the band gap to enhance the visible light absorption. This in situ ligand substitution method provides a promising approach to build a tunable platform for constructing high-performance MOF photocatalysts.