The
Role of Defects in Fe(II)–Goethite Electron
Transfer
Version 2 2018-02-20, 20:20
Version 1 2018-02-20, 20:18
Posted on 2018-02-20 - 20:20
Despite substantial experimental
evidence for Fe(II)–Fe(III)
oxide electron transfer, computational chemistry calculations suggest
that oxidation of sorbed Fe(II) by goethite is kinetically inhibited
on structurally perfect surfaces. We used a combination of 57Fe Mössbauer spectroscopy, synchrotron X-ray absorption and
magnetic circular dichroism (XAS/XMCD) spectroscopies to investigate
whether Fe(II)–goethite electron transfer is influenced by
defects. Specifically, Fe L-edge and O K-edge XAS indicates that the
outermost few Angstroms of goethite synthesized by low temperature
Fe(III) hydrolysis is iron deficient relative to oxygen, suggesting
the presence of defects from Fe vacancies. This nonstoichiometric
goethite undergoes facile Fe(II)–Fe(III) oxide electron transfer,
depositing additional goethite consistent with experimental precedent.
Hydrothermal treatment of this goethite, however, appears to remove
defects, decrease the amount of Fe(II) oxidation, and change the composition
of the oxidation product. When hydrothermally treated goethite was
ground, surface defect characteristics as well as the extent of electron
transfer were largely restored. Our findings suggest that surface
defects play a commanding role in Fe(II)–goethite redox interaction,
as predicted by computational chemistry. Moreover, it suggests that,
in the environment, the extent of this interaction will vary depending
on diagenetic history, local redox conditions, as well as being subject
to regeneration via seasonal fluctuations.
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Notini, Luiza; Latta, Drew E.; Neumann, Anke; Pearce, Carolyn I.; Sassi, Michel; N’Diaye, Alpha T.; et al. (2018). The
Role of Defects in Fe(II)–Goethite Electron
Transfer. ACS Publications. Collection. https://doi.org/10.1021/acs.est.7b05772
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AUTHORS (8)
LN
Luiza Notini
DL
Drew E. Latta
AN
Anke Neumann
CP
Carolyn I. Pearce
MS
Michel Sassi
AN
Alpha T. N’Diaye
KR
Kevin M. Rosso
MS
Michelle M. Scherer