title: Fenton chemistry at aqueous interfaces.
abstract: In a fundamental process throughout nature, reduced iron unleashes the oxidative power of hydrogen peroxide into reactive intermediates. However, notwithstanding much work, the mechanism by which Fe(2+) catalyzes H2O2 oxidations and the identity of the participating intermediates remain controversial. Here we report the prompt formation of O=Fe(IV)Cl3(-) and chloride-bridged di-iron O=Fe(IV) · Cl · Fe(II)Cl4(-) and O=Fe(IV) · Cl · Fe(III)Cl5(-) ferryl species, in addition to Fe(III)Cl4(-), on the surface of aqueous FeCl2 microjets exposed to gaseous H2O2 or O3 beams for <50 μs. The unambiguous identification of such species in situ via online electrospray mass spectrometry let us investigate their individual dependences on Fe(2+), H2O2, O3, and H(+) concentrations, and their responses to tert-butanol (an · OH scavenger) and DMSO (an O-atom acceptor) cosolutes. We found that (i) mass spectra are not affected by excess tert-butanol, i.e., the detected species are primary products whose formation does not involve · OH radicals, and (ii) the di-iron ferryls, but not O=Fe(IV)Cl3(-), can be fully quenched by DMSO under present conditions. We infer that interfacial Fe(H2O)n(2+) ions react with H2O2 and O3 >10(3) times faster than Fe(H2O)6(2+) in bulk water via a process that favors inner-sphere two-electron O-atom over outer-sphere one-electron transfers. The higher reactivity of di-iron ferryls vs. O=Fe(IV)Cl3(-) as O-atom donors implicates the electronic coupling of mixed-valence iron centers in the weakening of the Fe(IV)-O bond in poly-iron ferryl species.
authors.affiliation: The Hakubi Center for Advanced Research, Kyoto University, Kyoto 606-8302, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Enami
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Sakamoto
authors.forename: Agustín J
authors.initials: AJ
authors.lastname: Colussi
mesh_terms: D006861:Hydrogen Peroxide / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D058085:Iron Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D014867:Water / Q000737:chemistry*
chemical_list: C045076:Fenton's reagent; D058085:Iron Compounds; D014867:Water; D006861:Hydrogen Peroxide; D007501:Iron
keywords: advanced oxidation processes; aerosols; metal ions; nanoparticles; reactive oxygen species