Computational Molecular Simulation of the Oxidative Adsorption of Ferrous Iron at the Hematite (001)–Water Interface

Abstract

The interaction of Fe(II) with ferric oxide/oxyhydroxide phases is central to the biogeochemical redox chemistry of iron. Molecular simulation techniques were employed to determine the mechanisms and quantify the rates of Fe(II) oxidative adsorption at the hematite (001)-water interface. Molecular dynamics potential of mean force calculations of Fe(II) adsorbing on the hematite surface revealed the presence of three free energy minima corresponding to Fe(II) adsorbed in an outersphere complex, a monodentate innersphere complex, and a tridentate innersphere complex. The free energy barrier for adsorption from the outersphere position to the monodentate innersphere site was calculated to be similar to the activation enthalpy for water exchange around aqueous Fe(II). Adsorption at both innersphere sites was predicted to be unfavorable unless accompanied by release of protons. Molecular dynamics umbrella sampling simulations and ab initio cluster calculations were performed to determine the rates of electron transfer from Fe(II) adsorbed as an innersphere and outersphere complex. The electron transfer rates were calculated to range from 10 -4 to 10 2 s -1 , depending on the adsorption site and the Page 1 of 43 ACS Paragon Plus EnvironmentThe Journal of Physical Chemistry 2 potential parameter set, and were generally slower than those obtained in the bulk hematite lattice. The most reliable estimate of the rate of electron transfer from Fe(II) adsorbed as an outersphere complex to lattice Fe(III) was commensurate with the rate of adsorption as an innersphere complex suggesting that adsorption does not necessarily need to precede oxidation.

Visualizing the iron atom exchange front in the Fe(II)-catalyzed recrystallization of goethite by atom probe tomography

“…Major steps include (i) Fe(II) sorption, (ii) electron transfer (ET) between sorbed Fe(II) and lattice Fe(III) leading to their atom exchange (AE) at the interface, and (iii) conduction of injected electrons to different Fe(III) lattice sites, which then undergo (iv) reductive release as Fe(II). The sorption, ET, and conduction steps are strongly supported by 57 Fe−Mössbauer spectroscopy (12,13) and molecular simulations (14)(15)(16)(17)(18)(19). Thus, within individual mineral particles, recrystallized regions that capture the Fe isotopic composition of solution are predicted, comprising a record of the AE front.…”

Eighteen years of steel–bentonite interaction in the FEBEX in situ test at the Grimsel Test Site in Switzerland

“…Moreover, sorption of diffusing Fe 2+ on pre-existing Fe 3+ bearing oxides (e.g. on hematite (Yanina and Rosso 2008;Rosso et al 2010;Kerisit et al 2015) or goethite (Handler et al 2014)) followed by an electron transfer inside the oxide and a release of Fe 2+ from another crystallographic site is also possible. Redox interaction with the clay (edge or basal sorption and clay reduction) might lead to the formation of strongly sorbed Fe 3+ and immobile structural Fe 2+ (limited by the number of structural Fe(III) sites, i.e.…”

Concerted Metal Cation Desorption and Proton Transfer on Deprotonated Silica Surfaces

“…Here inner-sphere means direct contact between SiO − /M + , while outer-sphere is water-mediated adsorption,Atomic length-scale modeling can shed light on many aspects of cation adsorption. 9,[17][18][19][20] In particular, force field-based potential-of-mean-force (PMF) calculations have been successfully applied to study divalent metal cations desorption from mineral surfaces. 9,18 However, it is challenging to use non-electronic structure methods to model the interactions between transition metal (TM) cations and ligands.…”