MOFs-derived porous carbon embedded Fe⁰ nanoparticles as peroxymonosulfate activator for efficient degradation of organic pollutants

Achieving the harmless degradation of organic pollutants remains a challenging task for the advanced oxidation processes. Metal-organic frameworks have emerged in the field of energy and environmental catalysis. Herein, MIL-101(Fe) was employed as the precursor to prepare a porous carbon embedded Fe⁰ nanoparticles (Fe⁰@C) via a pyrolytic process under N₂ protection. MIL-101(Fe) and Fe⁰@C were characterized in detail by various instrumental techniques. The control experiments indicated that Fe⁰@C exhibited much higher capacity to activate peroxymonosulfate (PMS) for the degradation of Levofloxacin (LEV) than MIL-101(Fe). Within 60 min reaction time, LEV degradation efficiency was increased from 37.0% in the MIL-101(Fe)/PMS system to 96.3% in the Fe⁰@C/PMS one. The affecting parameters of Fe⁰@C/PMS system were investigated systematically, including LEV concentration, Fe⁰@C dosage, PMS dosage, solution pH and coexisting anions. Furthermore, various representative organic pollutants could be efficiently degraded in the Fe⁰@C/PMS system. Radical quenching tests and electron paramagnetic resonance (EPR) disclosed that singlet oxygen (¹O₂), sulfate radical (SO₄^•-) and hydroxyl radical (•OH) governed the degradation of LEV, among which ¹O₂ played the most prominent role. Meanwhile, the degradation intermediates and pathways of LEV under the radical and non-radical attacks were deduced by high-performance liquid chromatography-quadrupole-time of flight mass spectrometry (HPLC-QTOF/MS) assisted by density functional theory (DFT) calculations. The reasonably designed Fe⁰@C might facilitate electron transfer and thus promote Fe(III)/Fe(II) cycle and PMS activation. This work will provide a new idea for the development of MOFs-derived carbon-based persulfate activators.