Gallic Acid Accelerates the Oxidation Ability of the Peracetic Acid/Fe(III) System for Bisphenol A Removal: Fate of Various Radicals

Conveniently and cost-effectively obtained Fe(III) can be utilized for peracetic acid (PAA) activation in the presence of natural polyphenols. However, the effect of polyphenols on the fate of generated reactive oxygen species (ROS) remains unclear. In this study, it was demonstrated that Fe(III) can efficiently trigger PAA oxidation of pollutants with the assistance of gallic acid (GA), a widely distributed natural polyphenol. The GA/Fe(III)/PAA system efficiently removed bisphenol A (BPA) over a wide initial pH range of 4.0–7.0, with a removal rate of >90% over 20 min. Further, •OH played a dominant role in BPA degradation, and O2•– functioned as an intermediate contributing to the partial generation of •OH. The generated organic radicals (R-O•) did not considerably contribute to BPA removal. Apart from GA itself, both the reaction intermediates (phenoxy radicals) of GA with ROS and BPA degradation intermediates were crucial for the regeneration of Fe(II) from Fe(III) and the subsequent enhanced activation of PAA. Notably, further comprehensive analysis revealed an increase in •OH yield, but a decrease in R-O• production as the dosage of GA was increased from 10 to 100 μM. This finding emphasized the importance of properly utilizing GA, considering the reactivity of varied ROS toward different contaminants. R-O• (CH3CO2• and CH3CO3•) was quickly consumed by the GA-Fe(II) complex through single-electron transfer (SET) and/or by GA via H-abstraction (HAA). This study proposes a promising strategy for improving the Fe(III)/PAA process and advances the understanding of the trade-off between radical generation and elimination by polyphenols in PAA-based advanced oxidation processes (AOPs).