Monomer and micellar adsorptions of CTAB onto the clay/water interface

Abstract

In this study, the monomeric and micellar adsorption properties of clay samples in aqueous cetyltrimethylammonium bromide (CTAB) solutions were investigated as a function of ionic strength, CTAB equilibrium concentration, and temperature. It was found that the efficiency and effectiveness of CTAB adsorption decrease with increasing temperature, which is the exothermic nature of the adsorption. The sorption of CTAB onto clay increased at the pH range of 3–9 then the adsorbed amount did not change significantly in the range of pH 9–11. The isosteric adsorption enthalpy was found to be − 69.05 kJ/mol. Another observation was that the isotherm shape shifted from an L-shape to an S-shape with increasing temperature. The calculated entropy value (227.46 Jmol − 1 K − 1 ) was quite high and positive. The adsorption capacity increased with increasing ionic strength, as expected. The isotherm shapes for all electrolytes exhibited the change in the case of non-electrolyte and both the efficiency and effectiveness of adsorption decreased with increasing electrolyte concentration. The experimental data concerning adsorption of CTAB at 293 K were applied to the Langmuir model and a high fit was obtained, particularly for monomeric adsorption.