Engineering stable cd-based metal-organic framework photocatalysts via ligand pre-metallization and polynuclear clusters: enhanced charge separation for ciprofloxacin degradation.

To address environmental remediation challenges from ciprofloxacin (CIP), this study pioneers a ligand pre-metallization strategy diverging fundamentally from conventional post-synthetic approaches. By pre-constructing Fe-N coordination in Fe(III) meso-tetra(4-carboxyphenyl)porphine chloride (HTCPP(Fe)) ligands before assembly with Cd polynuclear clusters, a stable three-dimensional Fe-doped Cd-TCPP metal-organic framework (MOF) was engineered, overcoming pore collapse limitations in conventional porphyrinic MOFs. This coordination engineering enables triple synergistic mechanisms: (1) Metal-to-ligand charge transfer (MLCT)-enhanced light absorption, (2) built-in electric fields at FeN-Cd heterojunctions reducing charge-transfer resistance, and (3) high-density active sites accelerating hydroxyl radical (OH) production. The optimized system achieves near-complete CIP degradation within 25 min (maximum kinetic constant (k) = 0.40 min) under 10 W visible light and ultrafast solar degradation (99.2 % removal in 2.5 min, k = 1.92 min), surpassing state-of-the-art Fe-TCPP (k = 0.23 min). Mechanistic analysis via liquid chromatography-mass spectrometry (LC-MS) revealed piperazine cleavage/defluorination pathways, while ecological structure activity relationships (ECOSAR) verified reduced aquatic toxicity of intermediates. This work establishes a coordination-directed paradigm for precision MOF electronic engineering, offering a scalable solution for antibiotic remediation.