Ligand-length engineering in isoreticular Fe-MOFs enables efficient ciprofloxacin degradation

Abstract

Iron-based metal–organic frameworks (Fe-MOFs) are attractive photocatalysts for ciprofloxacin (CIP) degradation in photo-Fenton like reactions due to their accessible Fe sites and porous structures. However, the role of organic linkers in regulating degradation pathways remains unclear. Here, four Fe-MOFs with identical acs topology (MIL-88A, B, C, and D) were synthesised via ligand modulation and evaluated for visible-light-driven CIP degradation under ambient conditions. MIL-88A and MIL-88D achieved >90% degradation efficiency, yet followed distinct mechanisms. Quenching experiments, pH-dependent tests, and thermodynamic/kinetic analyses reveal that MIL-88A operates through a thermodynamically driven pathway enabled by a highly positive valence band, showing weak pH dependence. In contrast, MIL-88D proceeds via a kinetics-dominated photo-Fenton route, where efficient charge separation accelerates the Fe²⁺/Fe³⁺ redox cycle, leading to strong pH sensitivity. Degradation kinetic modeling further uncovers concentration-dependent dominance and pathway switching between the two routes. This work elucidates ligand-regulated thermodynamic–kinetic competition, offering design principles for advanced Fe-MOF photocatalysts for pollutant remediation.