Structure analysis of montmorillonite intercalated with rhodamine B: modeling and experiment

Abstract

The intercalation process and the structure of montmorillonite intercalated with [rhodamine B]⁺ cations have been investigated using molecular modeling (molecular mechanics and molecular dynamics simulations), X-ray powder diffraction and IR spectroscopy. The structure of the intercalate depends strongly on the concentration of rhodamine B in the intercalation solution. The presence of two phases in the intercalated structure was revealed by modeling and X-ray powder diffraction: (i) phase with basal spacing 18 Å and with bilayer arrangement of guests and (ii) phase with average basal spacing 23 Å and with monolayer arrangement of guests. In both phases the monomeric and dimeric arrangement can coexist in the interlayer space. Three types of dimers in the interlayer structure have been found by modeling: (i) H-dimer (head-to-head arrangement) present in the 18 Å phase, (ii) sandwich type of the head-to-tail arrangement (present in the 23 Å phase) and (iii) J-dimer (head-to-tail arrangement) present in the 23 Å phase.

Figure Montmorillonite intercalated with rhodamine B cations. On the left: phase 18 Å, bilayer dimeric arrangement of guests (H-dimers). On the right: phase 23 Å, monolayer arrangement of guests prepared using intercalation solution with a low concentration of rhodamine B