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Minerals 2017, 7(5), 78; https://doi.org/10.3390/min7050078

Na-Montmorillonite Edge Structure and Surface Complexes: An Atomistic Perspective

1
Department of Geology, Kangwon National University, Chuncheon 24341, Korea
2
Critical Zone Frontier Research Laboratory (CFRL), Kangwon National University, Chuncheon 24341, Korea
*
Author to whom correspondence should be addressed.
Academic Editor: Peng Yuan
Received: 3 April 2017 / Revised: 6 May 2017 / Accepted: 8 May 2017 / Published: 12 May 2017
(This article belongs to the Special Issue Computational Geochemistry)
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Abstract

The edges of montmorillonite (MMT) react strongly with metals and organic matter, but the atomic structure of the edge and its surface complexes are not unambiguous since the experimental isolation of the edge is challenging. In this study, we introduce an atomistic model of a Na MMT edge that is suitable for classical molecular dynamics (MD) simulations, in particular for the B edge, a representative edge surface of 2:1 phyllosilicates. Our model possesses the surface groups identified through density functional theory (DFT) geometry optimizations performed with variation in the structural charge deficit and Mg substitution sites. The edge structure of the classical MD simulations agreed well with previous DFT-based MD simulation results. Our MD simulations revealed an extensive H-bond network stabilizing the Na-MMT edge surface, which required an extensive simulation trajectory. Some Na counter ions formed inner-sphere complexes at two edge sites. The stronger edge site coincided with the exposed vacancy in the dioctahedral sheet; a weaker site was associated with the cleaved hexagonal cavity of the tetrahedral sheet. The six-coordinate Na complexes were not directly associated with the Mg edge site. Our simulations have demonstrated the heterogeneous surface structures, the distribution of edge surface groups, and the reactivity of the MMT edge. View Full-Text
Keywords: clay edge; mineral surface; Na-montmorillonite; nanoporous minerals; molecular dynamics; density functional theory; computational geochemistry clay edge; mineral surface; Na-montmorillonite; nanoporous minerals; molecular dynamics; density functional theory; computational geochemistry
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Newton, A.G.; Lee, J.-Y.; Kwon, K.D. Na-Montmorillonite Edge Structure and Surface Complexes: An Atomistic Perspective. Minerals 2017, 7, 78.

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