Structural properties of montmorillonite intercalated with tetraalkylammonium cations—Computational and experimental study

Several tetraalkylammonium (TAA) cations intercalated in layered clay mineral montmorillonite were studied by a combination of theoretical approach based on density functional theory (DFT) and infrared spectroscopy. DFT calculations revealed positions of TAA cations in the interlayer space and a dependence of d001 parameter on the cation size. A finite difference method and molecular dynamic simulations were used to analyze and interpret vibrational modes observed in the experimental spectra with a specific focus on the CH3 and CH2 stretching modes. MD simulations on the tetraethylammonium-montmorillonite (TEA-M) model showed a high sensitivity of the position of the stretching vibrations of the CH3 and CH2 groups on the d001 value. MD calculations also helped to distinguish vibrations of the parallel and perpendicular CH3 groups of the tetramethylammonium-montmorillonite (TMA-M) which was not possible from the experimental infrared spectra because of many overlapping broad bands.