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The Variable Capacitance Model: A Strategy for Treating Contrasting Charge-Neutralizing Capabilities of Counterions at the Mineral/Water Interface
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2014 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 8, 2009-2018 p.Article in journal (Refereed) Published
Abstract [en]

Thermodynamic models predicting ion adsorption at mineral/water interfaces can have limitations from the simplifying assumptions that compact plane thicknesses and capacitance values are constant, and that charge densities of electrolyte counterions of different charge-to-size ratios lie at the same planes of adsorption, or split between different planes. To address these limitations a thermodynamic adsorption modeling framework was developed to account for coexisting compact planes for each type of counterion complexes formed on a single mineral surface. This framework was developed to predict charge development at lepidocrocite (gamma-FeOOH) particle surfaces suspended in aqueous solutions of NaCl and NaClO4. The model incorporates properties of Cl-, ClO4-, and Na+ complexes formed at the (001) and (010) faces of this mineral obtained by molecular dynamics (MD) simulations. This concept was incorporated in a thermodynamic adsorption model that predicts an overall variable compact plane capacitance in terms of a linear combination of the capacitances of ion-specific EDL structures scaled for their relative surface loadings. These capacitance values are in turn constrained by compact plane thicknesses of every Cl-, ClO4-, and Na+ complex, based on their MD-derived structures and atomic densities. The model predicts experimental potential-determining (H+, OH-) data for submicrometer-sized synthetic lepidocrocite particles exhibiting both (001) and (010) faces. It also isolates electrostatic contributions from these faces. A computer code solving for this Variable Capacitance Model-VCM-is provided in the Supporting Information section of this article, and can be readily modified to predict molecular-level details of any other mineral/water interface systems using this methodology.

Place, publisher, year, edition, pages
Washington: American Chemical Society (ACS), 2014. Vol. 30, no 8, 2009-2018 p.
National Category
Chemical Sciences
URN: urn:nbn:se:umu:diva-87875DOI: 10.1021/la403938wISI: 000332494000012OAI: diva2:712533
Available from: 2014-04-15 Created: 2014-04-14 Last updated: 2014-04-15Bibliographically approved

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Boily, Jean-Francois
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