Theoretical and experimental study of montmorillonite intercalated with tetramethylammonium cation

Structural and vibrational features of Na-montmorillonite and montmorillonite intercalated with tetramethylammonium cation (TMA+) were characterized theoretically and experimentally. Theoretical study was performed using density functional theory with inclusion of dispersion corrections. The analysis of the hydrogen bonds in the calculated models has shown that the Na+ cations coordinated by six water molecules (Na-M model) are bound to montmorillonite layers by moderate hydrogen bonds between water molecules and basal oxygen atoms of the tetrahedral sheets. Hydrated Na+ cations are stabilized by relatively strong hydrogen bonds among water molecules. In the intercalate model, the TMA+ cation is fixed in the interlayer space by weak hydrogen bonds between the methyl groups and basal oxygen atoms of montmorillonite layers. The calculated vibrational spectra are in a good agreement with the measured infrared spectra. The detailed analysis of the simulated vibrational spectra allowed unambiguous identification of corresponding bands in the measured spectra and their assignment to the particular vibrational modes. For example, calculations clearly distinguished between AlMgOH and AlAlOH stretching vibrations and also between the coupled vibrations of the methyl groups of the TMA+ cations.

► DFT method is used on the models of Na+(H2O)6- and TMA+-montmorillonite structure. ► The dispersion corrections are involving in the calculations. ► The hydrogen bonds analysis is done in these intercalates. ► The calculated vibrational spectra are compared with experimental ones. ► The individual vibrations in the overlapped bands are analyzed in details.