Interactions between an acid-activated pillared clay and several organic cations including dyes (methylene blue, MB; crystal violet, CV; acriflavin, AF) and benzyl derivatives (benzyltrimethylammonium, BTMA; benzyltriethylammonium, 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 for CV. This mode of adsorption was interpreted in terms of interlayer adsorption with steric hindrance in the pillared galleries. On the other hand, when the dyes were adsorbed from high ionic strength solutions, adsorption levels well beyond the CEC of the clay could be reached, in particular for MB and CV. This was interpreted in terms of a second adsorption mode, involving formation of molecular aggregates on the outer surface of the clay, as evidenced by X-ray diffraction. The behavior of the cationic benzyl derivatives was markedly different, with an adsorption level always below the CEC and a decrease of adsorption as the ionic strength was increased, as expected for non-complex-forming cations.
Bibliographical noteFunding Information:
This research was supported by Grant 8803-1-96 of the Ministry of Science and Arts, Israel, and by the Association Franco-Israelienne pour la Recherche Scientifique et Technique (AFIRST) for French-Israeli collaboration. M. Vayer is gratefully acknowledged for performing the CEC determinations. We are very grateful to N. Papayannakos and N. Gangas for preparing the pillared clay in large quantities.
- Cation adsorption
- Charge reversal
- Ionic strength
- Movement organic cations
- Pillared clay
- X-ray diffraction