Effect of type and strength of electrolytes on the adsorption and adsolubilization into adsorbed CTAB on precipitated silica

Abstract

The aim of this research was to evaluate the adsorption and adsolubilization of acetophenone into cetyltrimethylammonium bromide (CTAB) adsorbed on precipitated silica with different electrolyte types (NaCl, MgCl2, MgSO4, and Na2CO3). The electrolyte concentration was varied in order to obtain better understanding of effect of electrolyte on adsorption and adsolubilization into CTAB adsorbed on silica. The presence of electrolytes resulted in a shift of the CTAB adsorption isotherm if the CTAB equilibrium concentration was lower than its CMC. The divalent anions had higher CTAB adsorption than the monovalent anions; whereas the presence of electrolytes reduced the maximum CTAB adsorption in the plateau region, according to the tendency to reduce the maximum CTAB adsorption, the electrolytes could be ranked as follows: NaCl > MgSO4 > Na2CO3 > MgCl2 possibly due to the competitive adsorption between the cation of surfactant and the cation of electrolyte onto the negatively charged sites of the silica. The CTAB adsorption and maximum CTAB adsorption increased with increasing electrolyte concentration. Moreover, the presence of electrolytes caused an increase of adsolubilization. The monovalent anion had higher adsolubilization of acetophenone than the divalent anion. However, electrolyte concentration had insignificant effect on the adsolubilization of acetophenone.