Boosted ciprofloxacin photoelectrocatalytic degradation using 7CN-Fe derived from Fe-based MOF cage: Establishment of diversified ROS system and enhanced electron transfer

Abstract

Treatment of pharmaceutical wastewater using efficient and energy-saving technology is urgently needed due to the universal existence of the emerging pollutants. Herein, 7CN-Fe, a carbon nanotube-restricted catalyst derived from MIL-101 (Fe), was prepared via co-calcination of the typical MOF cage with melamine. This process enabled the formation of Fe single-atom catalysts (Fe-SACs) and optimized the exposure of active sites for boosted ciprofloxacin (CIP) degradation in a photoelectrocatalytic system (PEC). The series of reactive sites, including CN-Fe, C-Fe, and Fe₃-C, contributed to the enhanced CIP degradation, with the kinetics of CN-Fe being 23.7-fold higher than those of MIL-101(Fe) (increasing from 0.0051 to 0.121 min⁻¹). Electron spin resonance (ESR) and quenching tests revealed that •OH, •O₂^-, h⁺, ¹O₂, and high valent iron (Hv-Fe) are contributors to CIP degradation, and among them, •O₂^- and ¹O₂ dominated the decomposition process. Density functional theory (DFT) analysis results manifested that the CN-Fe, C-Fe and Fe₃-C sites promoted the O₂ adsorption and the O-O bond length had extended. Among them, the Fe₃-C sites had the minimum O₂ adsorption energy (E_ads = -2.12 eV) and the O-O bond had the longest length (l_O-O = 1.432 Å) after activation. Based on the influence factors evaluation, cycling test, the degradation of various antibiotics, and the detection of iron ion leaching, the 7CN-Fe catalysts exhibited a promising application potential with the traits of wide adaptability and stable structure. This work provides a route for photoelectrocatalytic degradation system establishment by optimized MIL-101 (Fe) and singlet oxygen generation for efficient removal of organic contaminants.