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

High-valent iron\n(Fe(IV/V/VI)) has been widely applied in water\ndecontamination. However, common Fe(II)-activating oxidants including\nhydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and persulfate react\nslowly with Fe(II) and exhibit low selectivity for Fe(IV) production\ndue to the cogeneration of radicals. Herein, we report peroxyacids\n(POAs; R–C(O)OOH) that can react with Fe(II) more than 3 orders\nof magnitude faster than H<sub>2</sub>O<sub>2</sub>, with high selectivity\nfor Fe(IV) generation. Rapid degradation of bisphenol A (BPA, an endocrine\ndisruptor) was achieved by the combination of Fe(II) with performic\nacid (PFA), peracetic acid (PAA), or perpropionic acid (PPA) within\none second. Experiments with phenyl methyl sulfoxide (PMSO) and <i>tert</i>-butyl alcohol (TBA) revealed Fe(IV) as the major reactive\nspecies in all three Fe(II)-POA systems, with a minor contribution\nof radicals (i.e., <sup>•</sup>OH and R–C(O)O<sup>•</sup>). To understand the exceptionally high reactivity of POAs, a detailed\ncomputational comparison among the Fenton-like reactions with step-by-step\nthermodynamic evaluation was conducted. The high reactivity is attributed\nto the lower energy barriers for O–O bond cleavage, which is\ndetermined as the rate-limiting step for the Fenton-like reactions,\nand the thermodynamically favorable bidentate binding pathway of POA\nwith iron. Overall, this study advances knowledge on POAs as novel\nFenton-like reagents and sheds light on computational chemistry for\nthese systems.