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 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.