Co-intercalation of organic cations/amide molecules into montmorillonite with tunable hydrophobicity and swellability

Organo-montmorillonite (OMt) has been widely used in paints, drilling fluids, clay/polymer nanocomposites, adsorbents and biosensors, however the full potential of OMt is yet to be discovered. The co-introduction of cationic and nonionic species into Mt has great potential to expand modification strategies and applications of Mt However, details regarding the intercalation mechanism of dual organic species remain unclear and the aspects of hydrophobicity and swellability of OMt are unknown. In this work, the co-introduction into OMt of octadecyltrimethylammonium (ODTMA+) cations and a nonionic specie erucamide (EA), and ODTMA+ with an oleamide (OA). was investigated. The resultant OMt samples were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Hydrophobicity and swellability of the OMt were examined. The results showed that neither EA nor OA could be effectively introduced into the interlayer spaces of Mt, although adsorption of EA and OA onto the external surface of Mt did occur. In the presence of ODTMA+, however, both EA and OA were successfully co-intercalated into the interlayer spaces of Mt, and the basal spacing (d001) of ODTMA+, EA and OA co-intercalated OMt increased to as much as 4.2 nm. Such dual modification appeared to be effective at tailoring hydrophobicity. The swellability of ODTMA+, EA and OA co-intercalated OMt in xylene increased with the increase in the amount of EA and OA loaded. When Mt was modified using 1.0 CEC ODTMA+ with 0.5–1.75 CEC EA, 0.2 g OMt in 10 mL xylene swelled to take 10 ml volume, equating to a swell index of 100%. Here, a two-stage intercalation is proposed: cationic exchange of ODTMA+ to form a paraffin-type monolayer, followed by hydrophobic entropy-driven adsorption of nonionic EA and OA by intertwining organic chains into the interlayer spaces of the OMt The findings show the promise of co-intercalation to introduce many other cations and nonionic organic species into the interlayer spaces of Mt, and thus greatly expands the types of OMt for new applications.