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

Abstract

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 tert-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.