Mixed oxidation of chlorophene and 4-tert-butylphenol by ferrate(VI): Reaction kinetics, cross-coupling products and improved utilization efficiency of ferrate(VI)

Abstract

As two representative phenolic pollutants, chlorophene (CP) and 4-tert-butylphenol (4-tBP) are used in large quantities and could have adverse effects on aquatic organisms and even human health. Due to their co-occurrence in water and wastewater, the oxidative degradation of mixed solution of the two phenols by ferrate (Fe(VI)) was systematically investigated in this work. Compared with the single solution, the kapp values of CP and 4-tBP were increased by 15.7% and 91.9%, respectively in the mixed solution, and the calculated reaction stoichiometric efficiency (RSE) was also improved by more than one time. The reaction intermediates were identified by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis, from which three possible pathways including direct oxidation, oxygen transfer, ring opening and coupling reaction were proposed for mixed transformation of CP and 4-tBP in Fe(VI) system. The single/double oxygen transfer and single-electron transfer mechanism for the corresponding formation of hydroxylation products and coupling products from CP and 4-tBP were further elucidated by density functional theory (DFT) calculations. Since the cross-coupling reaction was more prone to occur than self-coupling reaction, the addition of another phenol promoted the conversion of the original phenol, leading to the increased kapp values of the two phenols in mixture solution. Finally, the salt bridge experiment also confirmed that the electron transfer between organic pollutants and Fe(VI) was enhanced in mixture solution of phenols. Findings of this study may provide useful information for eliminating co-existing water contaminants by Fe(VI).