Rapid and Highly Selective Fe(IV) Generation by Fe(II)-Peroxyacid Advanced Oxidation Processes: Mechanistic Investigation via Kinetics and Density Functional Theory

High-valent iron (Fe(IV/V/VI)) has been widely applied in water decontamination. However, common Fe(II)-activating oxidants including hydrogen peroxide (H₂O₂) and persulfate react slowly with Fe(II) and exhibit low selectivity for Fe(IV) production due to the cogeneration of radicals. Herein, we report peroxyacids (POAs; R-C(O)OOH) that can react with Fe(II) more than 3 orders of magnitude faster than H₂O₂, with high selectivity for Fe(IV) generation. Rapid degradation of bisphenol A (BPA, an endocrine disruptor) was achieved by the combination of Fe(II) with performic acid (PFA), peracetic acid (PAA), or perpropionic acid (PPA) within one second. Experiments with phenyl methyl sulfoxide (PMSO) and <i>tert</i>-butyl alcohol (TBA) revealed Fe(IV) as the major reactive species in all three Fe(II)-POA systems, with a minor contribution of radicals (i.e., ^•OH and R-C(O)O^•). To understand the exceptionally high reactivity of POAs, a detailed computational comparison among the Fenton-like reactions with step-by-step thermodynamic evaluation was conducted. The high reactivity is attributed to the lower energy barriers for O-O bond cleavage, which is determined as the rate-limiting step for the Fenton-like reactions, and the thermodynamically favorable bidentate binding pathway of POA with iron. Overall, this study advances knowledge on POAs as novel Fenton-like reagents and sheds light on computational chemistry for these systems.