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[摘要]：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 Si-29, Al-27, Mg-25, and H-1 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 H-1 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. |
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