Mixed adsorption of cationic and anionic surfactants from aqueous solution on silica gel

Abstract

The adsorption of dodecyltrimethylammonium bromide (DTAB), dodecylpyridinium bromide (DPB), sodium dodecylbenzenesulfonate (SDBS) and sodium dodecyl sulfate (SDS) from their single aqueous solutions and DTAB—SDBS and DPB—SDS binary mixed solutions on silica gel at 25°C has been investigated. The results show that the individual cationic surfactants can be adsorbed strongly onto the silica gel, but no significant adsorption of anionic surfactants can be detected. However, in the mixed systems, the adsorption amounts of both the cationic and anionic surfactant ions are enhanced, and the excess adsorption of cationic surface-active ions is exactly equal to the adsorption of anionic surface-active ions. Thus, it is reasonable to suggest that the excess adsorption of cationic and anionic surface-active ions is in the form of ion-pairs.