Functionalization of bentonite by intercalation of surfactants

Abstract

The functionalization of bentonite by intercalation of surfactants dodecylamine, hexadecylamine, octadecylamine, and the octadecyltrimethylammonium cation is described. Products are characterized by elemental analysis, thermal analysis, FT-IR spectra, and powder X-ray diffraction analysis. Laminar amine-clay nanocomposites contain about one mol amine per (Si,Al)(4) clay unit, while the cationic surfactant show an intercalation rate of only 0.42 under the same conditions. The cation insertion is governed by ion exchange and the resulting stoichiometry corresponds to the cationic exchange capacity of the clay. The stoichiometry of amine nanocomposites, going beyond the cationic exchange capacity, is explained by the insertion of amine species stabilized in the interlaminar phase by both, the coordination of sodium ions and van der Waals interactions between neutral surfactants. Models for the nanocomposite interlaminar space, considering the interlaminar distances, the geometry of the guest and the area available in aluminosilicates sheets, are proposed.