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Title: Structure and Charge Hopping Dynamics in Green Rust

Abstract

Green rust is a family of mixed-valent iron phases formed by a number of abiotic and biotic processes under alkaline suboxic conditions. Due to its high Fe2+ content, green rust is a potentially important phase for pollution remediation by serving as a powerful electron donor for reductive transformation. However, mechanisms of oxidation of this material are poorly understood. An essential component of the green rust structure is a mixed-valent brucite-like Fe(OH)2 sheet comprised of a two dimensional network of edge-sharing iron octahedra. Room temperature Mössbauer spectra show a characteristic signature for intermediate valence on the iron atoms in this sheet, indicative of a Fe2+-Fe3+ valence interchange reaction faster than approximately 107 s-1. Using Fe(OH)2 as structural analogue for reduced green rust, we performed Hartree-Fock calculations on periodic slab models and cluster representations to determine the structure and hopping mobility of Fe3+ hole polarons in this material, providing a first principles assessment of the Fe2+-Fe3+ valence interchange reaction rate. The calculations show that among three possible symmetry unique iron-to-iron hops within a sheet, a hop to next-nearest neighbors at an intermediate distance of 5.6 Å is the fastest. The predicted rate is on the order of 1012 s-1 consistent the Mössbauer-based constraint. Allmore » other possibilities, including hopping across interlayer spaces, are predicted to be slower than 107 s-1. Collectively, the findings suggest the possibility of hole self-diffusion along sheets as a mechanism for regeneration of lattice Fe2+ sites, consistent with previous experimental observations of edge-inward progressive oxidation of green rust.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
984251
Report Number(s):
PNNL-SA-55273
Journal ID: ISSN 1932-7447; 12701a; KP1504010; TRN: US1005246
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 111; Journal Issue: 30; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ATOMS; BINDING ENERGY; ELECTRONS; IRON; MOESSBAUER EFFECT; OXIDATION; POLARONS; POLLUTION; REACTION KINETICS; REGENERATION; SELF-DIFFUSION; SPECTRA; SYMMETRY; VALENCE; Environmental Molecular Sciences Laboratory

Citation Formats

Wander, Matthew C, Rosso, Kevin M, and Schoonen, Martin A. Structure and Charge Hopping Dynamics in Green Rust. United States: N. p., 2007. Web. doi:10.1021/jp072762n.
Wander, Matthew C, Rosso, Kevin M, & Schoonen, Martin A. Structure and Charge Hopping Dynamics in Green Rust. United States. https://doi.org/10.1021/jp072762n
Wander, Matthew C, Rosso, Kevin M, and Schoonen, Martin A. 2007. "Structure and Charge Hopping Dynamics in Green Rust". United States. https://doi.org/10.1021/jp072762n.
@article{osti_984251,
title = {Structure and Charge Hopping Dynamics in Green Rust},
author = {Wander, Matthew C and Rosso, Kevin M and Schoonen, Martin A},
abstractNote = {Green rust is a family of mixed-valent iron phases formed by a number of abiotic and biotic processes under alkaline suboxic conditions. Due to its high Fe2+ content, green rust is a potentially important phase for pollution remediation by serving as a powerful electron donor for reductive transformation. However, mechanisms of oxidation of this material are poorly understood. An essential component of the green rust structure is a mixed-valent brucite-like Fe(OH)2 sheet comprised of a two dimensional network of edge-sharing iron octahedra. Room temperature Mössbauer spectra show a characteristic signature for intermediate valence on the iron atoms in this sheet, indicative of a Fe2+-Fe3+ valence interchange reaction faster than approximately 107 s-1. Using Fe(OH)2 as structural analogue for reduced green rust, we performed Hartree-Fock calculations on periodic slab models and cluster representations to determine the structure and hopping mobility of Fe3+ hole polarons in this material, providing a first principles assessment of the Fe2+-Fe3+ valence interchange reaction rate. The calculations show that among three possible symmetry unique iron-to-iron hops within a sheet, a hop to next-nearest neighbors at an intermediate distance of 5.6 Å is the fastest. The predicted rate is on the order of 1012 s-1 consistent the Mössbauer-based constraint. All other possibilities, including hopping across interlayer spaces, are predicted to be slower than 107 s-1. Collectively, the findings suggest the possibility of hole self-diffusion along sheets as a mechanism for regeneration of lattice Fe2+ sites, consistent with previous experimental observations of edge-inward progressive oxidation of green rust.},
doi = {10.1021/jp072762n},
url = {https://www.osti.gov/biblio/984251}, journal = {Journal of Physical Chemistry. C},
issn = {1932-7447},
number = 30,
volume = 111,
place = {United States},
year = {Thu Aug 02 00:00:00 EDT 2007},
month = {Thu Aug 02 00:00:00 EDT 2007}
}