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

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• 作者：Sylvian Cadars ; R茅gis Gu茅gan ; Mounesha N. Garaga ; Xavier Bourrat ; Lydie Le Forestier ; Franck Fayon ; Tan Vu Huynh ; Teddy Allier ; Zalfa Nour ; Dominique Massiot
• 刊名：Chemistry of Materials
• 出版年：2012
• 出版时间：November 27, 2012
• 年：2012
• 卷：24
• 期：22
• 页码：4376-4389
• 全文大小：593K
• 年卷期：v.24,no.22(November 27, 2012)
• ISSN：1520-5002

文摘

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 noncrystalline 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 interlayer 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 nonrandom cationic distribution within the layers.

Keywords:

NMR; ab initio calculations; les+calculations&qsSearchArea=searchText">first-principles calculations; smectite; layered alumino-silicates; 2:1 clays