Peroxymonosulfate activation by iron(III)-tetraamidomacrocyclic ligand for degradation of organic pollutants via high-valent iron-oxo complex

Herein, we proposed a new catalytic oxidation system, i.e., iron(III)-tetraamidomacrocyclic ligand (Fem(III)-TAML) mediated activation of peroxymonosulfate (PMS), for highly efficient organic degradation using pchlorophenol (4-CP) as a model one. PMS/Fem(III)-TAML is capable of degrading 4-CP completely in 9 min at the initial 4-CP of 50 mu M and pH = 7, whereas the recently explored system, H2O2/Fem(III)-TAML, could only result in similar to 22% 4-CP removal in 20 min under otherwise identical conditions. More attractively, inorganic anions (i.e.,cl(-), SO42- , NO3-, and HCO3-) exhibited insignificant effect on 4-CP degradation, and the negative effect of natural organic matters (NOM) on the degradation of 4-CP in PMS/Fe-III-TAML is much weaker than the sulfate radical-based oxidation process (PMS/Co2+). Combined with in-situ XANES spectra, UV-visible spectra, electron paramagnetic resonance (EPR) spectra, and radical quenching experiments, high-valent iron-oxo complex (Fe-Iv(O)TAML) instead of singlet oxygen (O-1(2)), superoxide radical (O-2(center dot-)), sulfate radicals (SO4 center dot-) and hydroxyl radicals (HO center dot-) was the key active species responsible for 4-CP degradation. The formation rate (k(I)) and consumption rate (k(II)) of the Fe-Iv(O)TAML in PMS/Fem(III)-TAML were pH-dependent in the range of 6.0-11.5. As expected, increasing the Fem(III)-TAML and PMS dosage resulted in a higher steady-state concentration of Fe-Iv(O)TAML and enhanced the 4-CP degradation accordingly. In addition, the oxidation capacity of PMS was almost totally utilized in PMS/Fem(III)-TAML for 4-CP oxidation due to the two-electron abstraction from 4-CP by one PMS. We believe this study will shed new light on effective PMS activation by Fe-ligand complexes to efficiently degrade organic contaminants via nonradical pathway. (C) 2018 Elsevier Ltd. All rights reserved.