Interactions of monovalent organic cations with pillared clays

Interactions between an acid-activated pillared clay and several organic ca tions including dyes (methylene blue, MB; crystal violet, CV; acriflavin, A F) and benzyl derivatives (benzyltrimethylammonium, BTMA; benzyltriethylamm onium, BTEA) were studied by adsorption measurements and X-ray diffraction. When the dyes were adsorbed from low ionic strength solutions, adsorption was irreversible but saturated at levels below the cation exchange capacity (CEC) of the clay (0.6 meq/g). The difference with CEC value was largest f or CV. This mode of adsorption was interpreted in terms of interlayer adsor ption with steric hindrance in the pillared galleries. On the other hand, w hen the dyes were adsorbed from high ionic strength solutions, adsorption l evels well beyond the CEC of the clay could be reached, in particular for M B and CV. This was interpreted in terms of a second adsorption mode, involv ing formation of molecular aggregates on the outer surface of the clay, as evidenced by X-ray diffraction. The behavior of the cationic benzyl derivat ives was markedly different, with an adsorption level always below the CEC and a decrease of adsorption as the ionic strength was increased, as expect ed for non-complex forming cations. (C) 1999 Academic Press.