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 A and with bilayer arrangement of guests and (ii) phase with average basal spacing 23 A 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 A phase, (ii) sandwich type of the head-to-tail arrangement (present in the 23 A phase) and (iii) J-dimer (head-to-tail arrangement) present in the 23 A phase. Figure Montmorillonite intercalated with rhodamine B cations. On the left: phase 18 A, bilayer dimeric arrangement of guests (H-dimers). On the right: phase 23 A, monolayer arrangement of guests prepared using intercalation solution with a low concentration of rhodamine B

The rhodamine B intercalation of montmorillonite

“…Analysis of the calculated structure models confirmed the existence of two phases with different basal spacings d ∼ 1.8 and ∼ 2.3 nm revealed by X-ray diffraction [25] (see also Table 4 shows a summary of the results calculated for Models 1-4, i.e., the basal spacing, the total sublimation energy, and the van der Waals and electrostatic contributions related to one 3a × 2b × 1c supercell. As can be seen in Fig.…”

“…7. This structure with tilted monomers with the average basal spacing ∼2.3 nm was described in [25] and denoted as phase 2.3 nm. Calculated Models 2 and 3 are two examples of this phase.…”

“…A recent comparison of IR spectra for the host structure Na-montmorillonite and for montmorillonite intercalated with rhodamine B cations showed that the bands corresponding to the silicate layer remained unchanged after intercalation [25]. That means that the silicate layers can be treated as rigid bodies during energy minimization.…”

“…The strategy of modeling using an empirical force field was based on the experimental data (chemical analysis, IR spectroscopy, and X-ray powder diffraction [25]). The initial model for montmorillonite layer was built using structure data published by Tsipursky and Drits [26]: space group, C2/m.…”

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