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Iron Dissolution from Goethite (α-FeOOH) Surfaces in Water by Ab Initio Enhanced Free Energy Simulations

preprint
submitted on 18.04.2018 and posted on 19.04.2018 by Konstantin Klyukin, Kevin Rosso, Vitaly Alexandrov

Dissolution of redox-active metal oxides plays a key role in a variety of phenomena including (photo)electrocatalysis, degradation of battery materials, corrosion of metal oxides and biogeochemical cycling of metals in natural environments. Despite its widespread significance, mechanisms of metal-oxide dissolution remain poorly understood at the atomistic level. This study is aimed at elucidating the long-standing problem of iron dissolution from Fe(III)-oxide, a complex process involving coupled hydrolysis, surface protonation, electron transfer, and metal-oxygen bond cleavage. We examine the case of goethite (α-FeOOH), a representative phase bearing structural similarities with many other metal (hydr)oxides. By employing quantum molecular dynamics simulations (metadynamics combined with the Blue Moon ensemble approach), we unveil the mechanistic pathways and rates of both nonreductive and reductive dissolution of iron from the (110) and (021) goethite facets in aqueous solutions at room temperature. Our simulations reveal the interplay between concerted internal (structural) and external (from solution) protonation as essential for breaking Fe-O bonds, as well as for stabilizing intermediate configurations of dissolving Fe. We demonstrate specifically how Fe(III) reduction to Fe(II) yields higher dissolution rates than the proton-mediated pathway, while the most rapid dissolution is expected for these two processes combined, in agreement with experiments.

History

Email Address of Submitting Author

kklyukin2@unl.edu

Institution

University of Nebraska-Lincoln

Country

USA

ORCID For Submitting Author

0000-0001-8325-8725

Declaration of Conflict of Interest

no conflict of interest

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