New insights into the Fe(III)-activated peroxyacetic acid: Oxidation properties and mechanism

Iron-activated peroxyacetic acid (PAA) represents an innovative advanced oxidation process (AOP). However, the efficiency of PAA activation by Fe(III) is often underestimated due to the widespread assumption that Fe(III) exhibits much lower ability than Fe(II) to activate PAA. Herein, the oxidative degradation of Rhodamine B (RhB) by Fe(III)-activated PAA process was investigated, and some new insights into the performance and mechanism of the Fe(III)/PAA system were presented. Although the reaction rate of Fe(III) with PAA was slightly slower than that of Fe(II), Fe(III) was still able to activate PAA effectively, and the degradation efficiency of RhB was comparable to that of the Fe(II)/PAA system after 30 min of reaction. Notably, the Fe(III)/PAA system demonstrated superior oxidation capacity compared to conventional oxidant systems, including Fe(III)/H₂O₂, Fe(III)/PDS, Fe(III)/PMS. The degradation efficiency varied significantly across different water substrates. While Cl^- exhibited a certain inhibitory effect on the degradation of RhB, H₂PO₄^- exerted a pronounced inhibitory influence, whereas NO₃^-, SO₄^2- and HCO₃^- had negligible effects. The increase of humic acid (HA) showed a facilitating effect in the initial stage, followed by an inhibitory effect. Furthermore, mechanistic studies indicated that H₂O₂ in PAA solution was not effectively activated. The degradation of RhB primarily occurred through a non-radical pathway generated by PAA activation, with the contribution of reactive species (RS) in the order of Fe^IVO²⁺ > ^•OH > R-O^• (CH₃COO^• and CH₃COOO^•). RhB degradation was achieved not only by attacking the chromophore of RhB molecules, but also the effective destruction of the stable structures such as benzene rings. This study enhances the understanding of Fe(III)-activated PAA and broadens its potential for developing and applying PAA-based AOPs.