7 - Smectite Nanomaterials: Preparation, Properties, and Functional Applications

Abstract

The surface and the interlayer space of montmorillonite (Mt) can be modified and the interlayer space of Mt can be intercalated with guest cations through an ion-exchange reaction or other physical and chemical interactions. Typically, Ca2+ in the interlayer space of Ca2+-Mt can be replaced by cetyl trimethylammonium cation (CTA+, derived from surfactant cetyl trimethylammonium bromide CTAB) to yield organo-montmorillonite (OMt). Surfactant loaded on the unwashed OMt exists in multiple forms, which have more or less effects on its ability to swell and delamination of OMt in an organic solvent. Its ability to swell and the delamination of OMt in xylene primarily are affected by hydrophobic interactions between the alkyl chains of adsorbed CTAB surfactant (molecules and cations) on the OMt and xylene and the electrostatic interactions between neighboring edges of the OMt. A large volume of the particle networks of the OMt in xylene is formed due to multimode-connections, namely edge-to-edge, face-to-face, face-to-edge, and multifacial linking. The OMt provides distinct nanometer-scaled layers and interlayers for engineering it as selective adsorbents for adsorbing organic compounds. One example is the adsorption of Acid Red G (ARG) onto octadecyl trimethylammonium (OTA)-modified Mt for wastewater treatment. OMt can be exfoliated to nanolayers for producing clay/polymer nanocomposites. Exfoliating Mt for producing clay/polymer nanocomposites is mainly achieved through in situ exfoliation, solution exfoliation, and melt exfoliation. The Mt/polymer nanocomposites exhibit typically improved barrier properties, mechanical strength, thermal stability, and fire retardancy.