Selective Oxidation of Various Phenolic Contaminants by Activated Persulfate via the Hydrogen Abstraction Pathway: Fid-Bau Portal

Selective Oxidation of Various Phenolic Contaminants by Activated Persulfate via the Hydrogen Abstraction Pathway

Wang, Cong / Jia, Shao-Yi / Han, You / Li, Yang / Liu, Yong / Ren, Hai-Tao / Wu, Song-Hai / Han, Xu

Enzymatic polymerization of phenolic contaminants to polyphenolics by H₂O₂ is an effective method to turn phenolic wastes to useful polymers. However, the sensitivities and the high costs of enzymes always limit their applications in the long-run treatment of industrial wastewater. In this study, a highly efficient CuO-persulfate (PS) system is reported to be a promising candidate for enzyme–H₂O₂ and shows high reactivity to polymerize various phenolic contaminants to polymers under alkaline conditions with the ratio of PS/phenolics less than 2.0. Compared with the generally accepted mechanism that the oxidizing species of SO₄ ^•– and ·OH generated during PS activation primarily contribute to the oxidation of various organic contaminants, quenching experiments, EPR (electron paramagnetic resonance) analysis and DFT calculations in this study indicate that PS is activated on CuO via a nonradical pathway under alkaline conditions, and the O–O bond in PS is moderately elongated from 1.45 to 1.58 Å. The inversely linear relationship between log k _obs and BDE_O–H values of various phenolics in the Hammett plot confirms H-abstraction from various phenolics under alkaline conditions. DFT calculations further reveal the formation of phenolic radicals after the activated PS abstracts H from phenolic −OH, followed by subsequent polymerization of phenoxyl radicals to polyphenolics. Characterizations of the oxidation products confirm that more than 80% phenolic contaminants have been transformed to polyphenolics. This study provides a new alternative for recovering various phenolic contaminants from industrial wastewater.