Divergent performances of ZIF-67-derived Fe, Co, and FeCo catalysts in peroxymonosulfate activation: Mechanisms and application in ciprofloxacin degradation

Abstract The degradation of antibiotics in wastewater treatment poses a major and persistent challenge. In this study, we report the use of zeolitic imidazolate framework-67 (ZIF-67), a metal–organic framework (MOF), as a precursor for synthesizing three distinct catalysts (ZIF-67(Fe)-800, ZIF-67(Co)-800, and ZIF-67(FeCo)-800) through pyrolysis. These catalysts were employed to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation. Strikingly divergent catalytic performances were observed, with CIP degradation rate constants of 0.0027, 0.0731, and 0.0504 min–¹ for ZIF-67(Fe)-800, ZIF-67(Co)-800, and ZIF-67(FeCo)-800, respectively. Compared to PMS activation, these catalysts showed significantly reduced efficacy in activating peroxydisulfate and sodium percarbonate. Mechanistic investigations through electron paramagnetic resonance and quenching tests unambiguously identify hydroxyl radical (·OH), sulfate radical (SO₄•−), and singlet oxygen (¹O₂) as the dominant reactive species in ZIF-67(Fe)-800/PMS and ZIF-67(Co)-800/PMS systems. The ZIF-67(FeCo)-800/PMS system exhibited distinct behavior, with SO₄•− as the primary species accompanied by ·OH, ¹O₂, and superoxide radicals (O₂•−). Notably, H₂PO₄⁻ and HCO₃⁻ exhibited strong inhibitory effects on CIP degradation, while SO₄²⁻ and CH₃COO⁻ leaded to modest rate enhancements. Our findings establish a rational framework for designing MOF-derived catalysts, demonstrating their superior efficacy in advanced oxidation processes for pharmaceutical pollutant removal.