Coupling metal–organic frameworks and g-C₃N₄ to derive Fe@N-doped graphene-like carbon for peroxymonosulfate activation: Upgrading framework stability and performance

A highly active mediator (Fe@N-doped graphene-like carbon) for peroxymonosulfate (PMS) activation was prepared by employing g-C₃N₄ assisting NH₂-MIL-53(Fe) as the precursor. The addition of combined nitrogen sources (g-C₃N₄ and NH₂ groups) not only stabilized the phase composition and framework morphology, but also improved PMS activation performance significantly. In addition, the introduction of g-C₃N₄ increased the surface area. Electron paramagnetic resonance (EPR) spectroscopy and radical quenching experiments identified singlet oxygen (¹O₂), superoxide radicals (O₂^•−), hydroxyl radicals (•OH), and sulfate radicals (SO₄^•−) as the reactive oxygen species (ROS) in 4-aminobenzoic acid ethyl ether (ABEE) degradation via a combination process of nonradical and radical processes. The variable chemical valences of iron nanoparticles and quaternary-N, pyrrolic-N, pyridinic-N, and carbonyl (C=O) groups in the support contributed to the outstanding catalytic activity. A possible mechanism for PMS activation by Fe@N-doped graphene-like carbon for ABEE degradation was proposed, which involved sp² hybridized carbon and electron-rich sp² sites of the graphitic domain activating PMS via electron transfer. Intermediates were identified using liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS). The degradation pathway of ABEE was reported for the first time in the advanced oxidation process field. Based on intermediate identification of sulfamethoxazole (SMX) degradation, six intermediates were first reported and a new reaction pathway established. This work provides a promising approach to the rational design of high-performance active mediators for environmental remediation.