Rethinking Arsenate Coordination at the Surface of Goethite
(2009) In Chemistry: A European Journal 15(20). p.5063-5072- Abstract
- A fundamental precept of geochemistry is that arsenate coordinates at mineral surfaces in a predominately bridging-bidentate fashion. We show that this is incorrect for the model system, arsenate adsorbed at the surface of goethite (alpha-FeOOH), using a combination of XRD, EXAFS, and IR spectroscopic results. We report the crystal structure of pentaamminecobalt(III) arsenate, which consists of monodentate-coordinated metal-arsenato complexes that have Co-As distances of only 3.25 angstrom. This result implies that metal-arsenic distances are not diagnostic for the coordination mode of arsenate. We show that the K-edge EXAFS spectra of pentaamminecobalt(ill) arsenate and arsenate-goethite surface complexes are strikingly similar, which... (More)
- A fundamental precept of geochemistry is that arsenate coordinates at mineral surfaces in a predominately bridging-bidentate fashion. We show that this is incorrect for the model system, arsenate adsorbed at the surface of goethite (alpha-FeOOH), using a combination of XRD, EXAFS, and IR spectroscopic results. We report the crystal structure of pentaamminecobalt(III) arsenate, which consists of monodentate-coordinated metal-arsenato complexes that have Co-As distances of only 3.25 angstrom. This result implies that metal-arsenic distances are not diagnostic for the coordination mode of arsenate. We show that the K-edge EXAFS spectra of pentaamminecobalt(ill) arsenate and arsenate-goethite surface complexes are strikingly similar, which suggests that arsenate could be coordinated at the goethite surface in a monodentate fashion. Refinements of the k(3)-weighted EXAFS spectra of arsenate adsorbed on goethite results in values of CNAs-Fe between 0.8-1.1 (+/- 0.7), and there is no evidence that the coordination mode of arsenate changes as a function of pH or arsenate surface coverage. We report IR spectra from the first simultaneous IR and potentiometric titration of arsenate adsorbed on deuterated goethite (alpha-FeOOD) in D2O, and we show for the first time the As-O stretching bands of arsenate-goethite surface complexes. We deduce that arsenate-goethite surface complexes are un-, singly, or doubly protonated, depending on pH, from a principal component analysis of the As-O stretching region and an interpretation of the Type-B OH stretching region. In summary, our cumulative results show that arsenate coordinates at the water-goethite interface in a predominately monodentate fashion. Furthermore, we find no evidence for bridging-bidentate coordination, which is a finding that impacts oxoanion bioavailability and challenges theories of mineral dissolution and surface complexation. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/1425334
- author
- Loring, John S. ; Sandstrom, Malin H. ; Norén, Katarina LU and Persson, Per LU
- organization
- publishing date
- 2009
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- surface chemistry, goethite, geochemistry, arsenate, coordination modes
- in
- Chemistry: A European Journal
- volume
- 15
- issue
- 20
- pages
- 5063 - 5072
- publisher
- Wiley-Blackwell
- external identifiers
-
- wos:000266292200014
- scopus:66149091115
- pmid:19334024
- ISSN
- 1521-3765
- DOI
- 10.1002/chem.200900284
- language
- English
- LU publication?
- yes
- id
- 685b74a7-af4d-453f-9e26-a07e0590e30e (old id 1425334)
- date added to LUP
- 2016-04-01 13:19:40
- date last changed
- 2022-07-15 23:04:06
@article{685b74a7-af4d-453f-9e26-a07e0590e30e,
abstract = {{A fundamental precept of geochemistry is that arsenate coordinates at mineral surfaces in a predominately bridging-bidentate fashion. We show that this is incorrect for the model system, arsenate adsorbed at the surface of goethite (alpha-FeOOH), using a combination of XRD, EXAFS, and IR spectroscopic results. We report the crystal structure of pentaamminecobalt(III) arsenate, which consists of monodentate-coordinated metal-arsenato complexes that have Co-As distances of only 3.25 angstrom. This result implies that metal-arsenic distances are not diagnostic for the coordination mode of arsenate. We show that the K-edge EXAFS spectra of pentaamminecobalt(ill) arsenate and arsenate-goethite surface complexes are strikingly similar, which suggests that arsenate could be coordinated at the goethite surface in a monodentate fashion. Refinements of the k(3)-weighted EXAFS spectra of arsenate adsorbed on goethite results in values of CNAs-Fe between 0.8-1.1 (+/- 0.7), and there is no evidence that the coordination mode of arsenate changes as a function of pH or arsenate surface coverage. We report IR spectra from the first simultaneous IR and potentiometric titration of arsenate adsorbed on deuterated goethite (alpha-FeOOD) in D2O, and we show for the first time the As-O stretching bands of arsenate-goethite surface complexes. We deduce that arsenate-goethite surface complexes are un-, singly, or doubly protonated, depending on pH, from a principal component analysis of the As-O stretching region and an interpretation of the Type-B OH stretching region. In summary, our cumulative results show that arsenate coordinates at the water-goethite interface in a predominately monodentate fashion. Furthermore, we find no evidence for bridging-bidentate coordination, which is a finding that impacts oxoanion bioavailability and challenges theories of mineral dissolution and surface complexation.}},
author = {{Loring, John S. and Sandstrom, Malin H. and Norén, Katarina and Persson, Per}},
issn = {{1521-3765}},
keywords = {{surface chemistry; goethite; geochemistry; arsenate; coordination modes}},
language = {{eng}},
number = {{20}},
pages = {{5063--5072}},
publisher = {{Wiley-Blackwell}},
series = {{Chemistry: A European Journal}},
title = {{Rethinking Arsenate Coordination at the Surface of Goethite}},
url = {{http://dx.doi.org/10.1002/chem.200900284}},
doi = {{10.1002/chem.200900284}},
volume = {{15}},
year = {{2009}},
}