The Fe(II) auto-catalyzed reduction-oxidation transformation of iron oxides and its manifestation into various final particle phases and morphologies are fascinating phenomena,1,2 which, however, remain poorly understood on the molecular level. Despite the recent insight gained by the Fe-isotopic exchange assays,1,2 a comprehensive atomistic model is yet to be developed. To link the isotopic assay observations with the essential elementary processes occurring on the molecular scale we developed a Kinetic Monte Carlo modeling framework that takes into account all available details of the interfacial oxide redox transformation, electron/proton transfer, interfacial electrostatics and the crystal-face specific reactivity.3-6 In particular, we focus on coupling between apparently independent events: oxidative adsorption of Fe(II) and reductive detachment of surface-exposed Fe(III) ions. We found that subtle charge flows in the interfacial and subsurface regions contribute to the interdependence of these events and can induce subtle morphological changes in iron oxide nanoparticles. Our results are important for improving our understanding the geochemical iron cycling in environment, and shed new light on the surface and bulk mediated coupling between reactivity and electrostatics of iron oxides responding to the influence of a redox gradient. 1Handler, R. M.; et al. Fe(II)-Catalyzed Recrystallization of Goethite Revisited. Environ. Sci. Technol. 2014, 48, 11302–11311. 2Frierdich, A. J.; et al. Helgeson, M.; Liu, C.; Wang, C. Iron Atom Exchange Between Hematite and Aqueous Fe (II). Environ. Sci. Technol. 2015, 49, 8479–8486. 3Chatman, S.; Zarzycki, P.; Rosso, K. M. Surface Potentials of (001), (012), (113) Hematite (α-Fe2O3) Crystal Faces in Aqueous Solution. Phys. Chem. Chem. Phys. 2013, 15, 13911–13911. 4Zarzycki, P.; Chatman, S.; Preocanin, T.; Rosso, K. M. Electrostatic Potential of Specific Mineral Faces. Langmuir 2011, 27, 7986–7990. 5Zarzycki, P.; Kerisit, S.; Rosso, K. M. Molecular Dynamics Study of Fe(II) Adsorption, Electron Exchange, and Mobility at Goethite (α-FeOOH) Surfaces. J. Phys. Chem. C 2015, 119, 3111–3123. 6Zarzycki, P.; Smith, D. M.; Rosso, K. M. Proton Dynamics on Goethite Nanoparticles and Coupling to Electron Transport. J. Chem. Theory Comput. 2015, 11, 1715–1724.

Kinetic Monte Carlo study of interfacial Fe-isotope exchange in the redox transformation of iron(III) oxides

251st National Meeting (2016)

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