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 (FeIII -TAML) mediated activation of peroxymonosulfate (PMS), for highly efficient organic degradation using p-chlorophenol (4-CP) as a model one. PMS/FeIII -TAML is capable of degrading 4-CP completely in 9 min at the initial 4-CP of 50 μM and pH = 7, whereas the recently explored system, H2 O2 /FeIII -TAML, could only result in ∼22% 4-CP removal in 20 min under otherwise identical conditions. More attractively, inorganic anions (i.e., Cl- , SO4 2- , 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/FeIII -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 (FeIV (O)TAML) instead of singlet oxygen (1 O2 ), superoxide radical (O2 •- ), sulfate radicals (SO4 •- ) and hydroxyl radicals (HO• ) was the key active species responsible for 4-CP degradation. The formation rate (kI ) and consumption rate (kII ) of the FeIV (O)TAML in PMS/FeIII -TAML were pH-dependent in the range of 6.0-11.5. As expected, increasing the FeIII -TAML and PMS dosage resulted in a higher steady-state concentration of FeIV (O)TAML and enhanced the 4-CP degradation accordingly. In addition, the oxidation capacity of PMS was almost totally utilized in PMS/FeIII -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.