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Binding geometries of silicate species on ferrihydrite surfaces
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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2018 (English)In: ACS EARTH AND SPACE CHEMISTRY, ISSN 2472-3452, Vol. 2, no 2, p. 125-134Article in journal (Refereed) Published
Abstract [en]

Silicate sorption on ferrihydrite surfaces, as monomers, oligomers, and polymers, strongly affects ferrihydrite crystallinity, thermodynamic stability, and surface reactivity. How these silicate species bind on ferrihydrite surfaces is, however, not well understood. We have determined silicate binding geometries using a combination of X-ray absorption spectroscopy (XAS), differential atomic pair distribution function (d-PDF) analysis, and density functional theory (DFT) calculations. Silicon K-edge absorption pre edges and DFT-predicted energies indicate that silicate forms monomeric monodentate mononuclear (MM) complexes at low silicate sorption loadings. With increasing silicate loading, the pre-edge peak shifts to higher energies, suggesting changes in the silicate binding geometry toward multidentate complexation. The d-PDF analysis determines the Si Fe interatomic distance to be 3.25 A for the high-loading samples. The DFT calculations indicate that such distance corresponds to an oligomer in the bidentate binuclear (BB) binding geometry. The transition of the silicate sorption geometry accompanied by polymerization can affect stability of ferrihydrite and its adsorption and redox reactivity and increase the degree of Si isotopic fractionation upon silicate sorption on Fe oxides. MM monomeric complexes and BB oligomeric complexes should be used for surface complexation models predicting silicate sorption on Fe oxide surfaces.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC , 2018. Vol. 2, no 2, p. 125-134
Keywords [en]
silicate, ferrihydrite, binding geometry, polymerization, Si K-edge LINES spectroscopy, differential PDF alysis, DFT calculations
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-145786DOI: 10.1021/acsearthspacechem.7b00109ISI: 000425569600006OAI: oai:DiVA.org:umu-145786DiVA, id: diva2:1192460
Available from: 2018-03-22 Created: 2018-03-22 Last updated: 2018-06-09Bibliographically approved

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Boily, Jean-Francois

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CiteExportLink to record
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Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
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  • Other style
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  • de-DE
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Output format
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  • asciidoc
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