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 (O-1(2)), superoxide radicals (O-2(center dot-)), hydroxyl radicals (center dot OH), and sulfate radicals (SO4 center dot-) 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 = 0) 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 sp(2) hybridized carbon and electron-rich sp(2) 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.