HMIL@ZIF-67/SiC Composite with MOFs-on-MOFs Structure for Activated Persulfate Degradation of Ciprofloxacin

To address the challenge of thoroughly removing the antibiotic ciprofloxacin (CIP) using conventional processes, this study employed a MOFs-on-MOFs strategy. Utilizing silicon carbide (SiC) as the electron transport medium, cobalt-based zeolite imidazolate framework (ZIF-67) was in situ formed on the surface of a titanium-based metal-organic framework (MIL-125). This approach successfully constructed the MIL@ZIF-67/SiC ternary heterojunction composite. Characterization revealed that this material significantly suppressed metal ion leaching by forming Ti-O-Co bonds, while the introduction of SiC effectively promoted interfacial charge transfer. Performance evaluation demonstrated that the optimized MIL@ZIF-67/SiC catalyst (1:2 ratio) achieved over 96% CIP degradation within 30 min, exhibiting broad-spectrum degradation capabilities toward pollutants including tetracycline and Rhodamine B. Mechanistic analyses suggest that the Co²⁺/Co³⁺ redox cycle in ZIF-67 plays a central role in PMS activation and reactive oxygen species generation. Titanium oxide clusters in MIL-125 regulate the electron density at cobalt sites via interfacial charge transfer, while the incorporation of SiC is proposed to facilitate interfacial electron transfer and promote the regeneration of Co²⁺ from Co³⁺. These results suggest that the synergistic interaction among MIL-125, ZIF-67, and SiC facilitates PMS activation and sustains the catalytic redox process. Density functional theory calculations were employed to identify the reactive sites of CIP molecules. This study provides new insights for designing multimetal MOF heterojunction environmental functional materials.