STRUCTURAL FEATURES OF MONTMORILLONITE-SURFACTANT SYSTEMS: INFLUENCE OF SURFACTANT PACKING DENSITY AND MONTMORILLONITE SURFACE NATURE

Abstract

This study presents sorption investigations of complexes formed by dihexadecyldimethylammonium bromide (DHDAB) and hexadecyltrimethylammonium bromide (HDTMAB) with montmorillonite, revealing the high affinity of these complexes for the interlayer space of clay. The intercalation process involves several stages, including initial rapid saturation, the formation of saturation plateaus, and subsequent super-equivalent sorption linked to the development of multi-layered structures or micelle-like formations on the surface of clay plates. This sorption mechanism is similar for various cationic surfactants.
DHDAB, with two alkyl chains, exhibits a more complex intercalation dynamic compared to HDTMAB, which has only one chain, and shows higher saturation efficiency at early stages. The cation exchange capacity (CEC) of montmorillonite influences the intercalation process, with clays possessing lower CEC having fewer available sites for intercalation.
Adsorption of different amounts of surfactants results in crystalline structures with varying interlayer distances. The saturation level of exchangeable cations (n) influences the interplanar distance, and increasing n leads to a reduction in the specific surface area of montmorillonite samples. The adsorption efficiency of methylene blue on montmorillonites depends on their cation exchange capacity, structure, and degree of surfactant saturation. However, excessive saturation may lead to decreased efficiency due to the blocking of interlayer space. These findings are significant for the development and optimization of montmorillonite-based materials for environmental sorption and purification.