Interfacial construction of Co-MOF/NiCu-MOF for enhanced visible-light-driven peroxymonosulfate activation and ciprofloxacin degradation: Mechanistic insights, kinetics and stability study

Photocatalysts based on metal–organic frameworks (MOFs) have garnered significant interest for enhanced advanced oxidation processes; yet, inadequate charge separation and limited availability of redox-active sites continue to impede their catalytic performance. A hierarchical Co-MOF/NiCu-MOF heterostructure was synthesised using an in-situ MOF-on-MOF growth strategy and employed for visible-light-assisted activation of peroxymonosulfate (PMS) to effectively degrade pharmaceutical contaminants. The integration of Co-MOF with bimetallic NiCu-MOF resulted in an interfacially linked framework exhibiting improved visible-light absorption, hierarchical structure, plentiful Co/Ni/Cu redox centers, and expedited interfacial charge transfer. The Co-MOF/NiCu-MOF demonstrated significantly enhanced catalytic activity relative to individual Co-MOF, Ni-MOF, Cu-MOF, and NiCu-MOF. Under optimized conditions, the Co-MOF/NiCu-MOF/PMS/visible-light system attained 98.2% ciprofloxacin (CIP) degradation with a pseudo-first-order rate constant of 0.1312 min −1 . The catalytic activity was significantly influenced by PMS dosage, catalyst loading, pH, CIP concentration, interfering species, and water matrix. The system exhibited superior performance in both tap water and simulated wastewater, indicating strong practical application. Radical quenching experiments and EPR analysis established that OH • was the predominant oxidative species, along with the minor contribution of SO 4 • ‾ and 1 O 2 to the degradation process. Mass Spectrometry analysis indicated that the CIP underwent degradation via sequential hydroxylation, oxidation, side-chain cleavage, ring-opening, and mineralisation processes. The catalyst maintained 96.3% degradation efficiency after five cycles with minimal metal leaching, indicating exceptional stability and reusability. This study emphasises MOF-on-MOF interfacial engineering as a proficient approach for developing effective PMS activators for the remediation of pharmaceutical wastewater.