title: Formation of environmentally persistent free radical (EPFR) in iron(III) cation-exchanged smectite clay.
abstract: Environmentally persistent free radicals (EPFRs) have been found at a number of Superfund sites, with EPFRs being formed via a proposed redox process at ambient environmental conditions. The possibility of such a redox process taking place at ambient environmental conditions is studied utilizing a surrogate soil system of phenol and iron(III)-exchanged calcium montmorillonite clay, Fe(III)CaM. Sorption of phenol by the Fe(III)CaM is demonstrated by Fourier-transformed infra-red (FT-IR) spectroscopy, as evidenced by the peaks between 1345 cm(-1) and 1595 cm(-1), and at lower frequencies between 694 cm(-1) and 806 cm(-1), as well as X-ray diffraction (XRD) spectroscopy, as shown by an increase in interlayer spacing within Fe(III)CaM. The formation and characterization of the EPFRs is determined by electron paramagnetic resonance (EPR) spectroscopy, showing phenoxyl-type radical with a g-factor of 2.0034 and ΔHP-P of 6.1 G at an average concentration of 7.5 × 10(17) spins per g. EPFRs lifetime data are indicative of oxygen and water molecules being responsible for EPFR decay. The change in the oxidation state of the iron redox center is studied by X-ray absorption near-edge structure (XANES) spectroscopy, showing that 23% of the Fe(III) is reduced to Fe(II). X-ray photoemission spectroscopy (XPS) results confirm the XANES results. These findings, when combined with the EPFR concentration data, demonstrate that the stoichiometry of the EPFR formation under the conditions of this study is 1.5 × 10(-2) spins per Fe(II) atom.
authors.affiliation: Louisiana State University, Department of Chemistry, Baton Rouge, LA 70803, USA. rlcook@lsu.edu and Louisiana State University Superfund Research Center, Baton Rouge, Louisiana 70803, USA.
authors.forename: Ugwumsinachi G
authors.initials: UG
authors.lastname: Nwosu
authors.affiliation: Centre for Advanced Microstructures & Devices, Louisiana State University, 6980 Jefferson Highway, Baton Rouge, Louisiana 70806, USA.
authors.forename: Amitava
authors.initials: A
authors.lastname: Roy
authors.affiliation: Louisiana State University, Department of Chemistry, Baton Rouge, LA 70803, USA. rlcook@lsu.edu and Louisiana State University Superfund Research Center, Baton Rouge, Louisiana 70803, USA.
authors.forename: Albert Leo N
authors.initials: AL
authors.lastname: dela Cruz
authors.affiliation: Louisiana State University, Department of Chemistry, Baton Rouge, LA 70803, USA. rlcook@lsu.edu and Louisiana State University Superfund Research Center, Baton Rouge, Louisiana 70803, USA.
authors.forename: Barry
authors.initials: B
authors.lastname: Dellinger
authors.affiliation: Louisiana State University, Department of Chemistry, Baton Rouge, LA 70803, USA. rlcook@lsu.edu and Louisiana State University Superfund Research Center, Baton Rouge, Louisiana 70803, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Cook
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D000077215:Clay; D005609:Free Radicals / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008956:Models, Chemical; D017640:Silicates / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D005609:Free Radicals; D017640:Silicates; C033214:Smectite; D007501:Iron; D000077215:Clay