Coadsorption of Naphthalene Derivatives and Cetyltrimethylammonium Bromide on Alumina/Water, Titanium Dioxide/Water, and Silica/Water Interfaces

Abstract

The adsorption of cetyltrimethylamonium bromide at silica/water, alumina/water, and titanium dioxide/water interfaces has been determined at pH values for which these hydrophilic surfaces are all negatively charged. Then the coadsorption of 2(2-naphthyl) ethanol and 1-napthylamine onto the surfactant aggregates was investigated both below and above the critical micelle concentration (cmc). The solute uptake from the aqueous solution increases with surfactant surface coverage up to the cmc and decreases above the cmc as the result of free micelle formation and preferential micellar solubilization. Solute partition coefficients were determined both for the coadsorption and the micellar solubilization effects. Within experimental uncertainty, the coadsorption partition coefficient for each solute is independent of the solid substrate employed. It is solely a function of the surfactant adsorption and of the neutral solute properties. The coadsorption partition coefficient is equal to the micellar solubilization constant for the alcohol, but a ratio of about 2 in favor of the coadsorption constant is found for the amine. The possible origin of this effect is discussed.