Fe–N coordination induced electronic modulation of Fe-MOFs for efficient peroxymonosulfate activation and singlet oxygen-mediated degradation of metronidazole

Enhancing the electron transfer capability of Fe sites in iron-based metal-organic frameworks (Fe-MOFs) is crucial for improving their catalytic performance in peroxymonosulfate (PMS) activation. In this study, a mixed-ligand strategy was employed to modulate the coordination environment of Fe sites by using 1,3,5-benzenetricarboxylic acid (H₃BTC) and p -phenylenediamine (PPD) as mixed ligands, yielding a series of dual-ligand Fe-MOF catalysts (Fe-BTCₓ-PPDᵧ). Among the prepared catalysts, Fe-BTC₆₀-PPD₄₀ exhibited the highest catalytic activity, achieving over 99% removal of metronidazole (MNZ) within 60 min and the degradation process followed pseudo-first-order kinetics with a rate constant of 0.078 min −1 (11.8 times that of pristine Fe-BTC). Comprehensive characterizations, combined with density functional theory (DFT) calculations and reactive species identification, revealed that the introduction of PPD formed Fe N coordination structures, which increased the electron density at Fe sites, enhanced the electron transfer capability of the catalyst, and enabled efficient PMS activation with nearly 100% selectivity toward singlet oxygen ( 1 O₂) generation. The Fe-BTC₆₀-PPD₄₀ exhibits satisfactory durability and stability. The Fe-BTC₆₀-PPD₄₀/PMS system demonstrated broad pH adaptability (3−11), strong resistance to coexisting inorganic anions and organic matter. Furthermore, immobilization of Fe-BTC₆₀-PPD₄₀ onto quartz sand (QS) yielded a macroscale catalytic material (Fe-BTC₆₀-PPD₄₀@QS), alleviating the issues of agglomeration and difficult recovery of powder catalysts in water treatment applications. This work provides a feasible strategy for designing high-performance Fe-MOF-based heterogeneous catalysts for PMS activation and offers insights into the non-radical degradation mechanism for efficient water treatment.