New Insights into the Molecular Structures, Compositions, and Cation Distributions in Synthetic and Natural Montmorillonite Clays

Abstract : We present a detailed investigation of the molecular structure of montmorillonite, an aluminosilicate clay with important applications in materials sciences, such as for catalysis, drug delivery, or as a waste barrier. Solid-state 29Si, 27Al, 25Mg, and 1H nuclear magnetic resonance (NMR) measurements combined with density functional theory (DFT) calculations provide a comprehensive picture of the local structure and composition of a synthetic clay and its naturally-occurring analogue. A revised composition is proposed based on NMR results that allow the identification and quantification of the signatures of otherwise undetectable non-crystalline impurities, thus largely complementing the traditional elemental analyses. Solid-state 1H NMR at fast magic-angle spinning (MAS) and high magnetic field provide quantitative information on intra- and inter-layer local environments that are crucial for the determination of the amount of Mg/Al substitution within the octahedral layer. In combination with DFT calculations of energies, it suggests that pairs of adjacent Mg atoms are unfavorable, leading to a non-random cationic distribution within the layers.
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Sylvian Cadars, Régis Guégan, Mounesha N Garaga, Xavier Bourrat, Lydie Le Forestier, et al.. New Insights into the Molecular Structures, Compositions, and Cation Distributions in Synthetic and Natural Montmorillonite Clays. Chemistry of Materials, American Chemical Society, 2012, 24, pp.4376-4389. ⟨10.1021/cm302549k⟩. ⟨hal-00749159⟩

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