Coadsorption of Naphthalene Derivatives and Cationic Surfactants on Porous Silica in Aqueous Solutions

Abstract

The coadsorption of cationic surfactants and several naphthalene derivatives on a porous silica, Sorbsil C30, has been investigated in aqueous solutions as a function of surfactant concentration below and above the critical micelle concentration (cmc) at two pH values. 2-Naphthol and 2-(2-naphthyl)ethanol are not adsorbed onto the silica surface. Adsorption of cetylpyridinium chloride or cetyltrimethylammonium bromide on the silica induces a considerable coadsorption of the neutral molecules. The effect may be described by a partitioning process. Above the cmc, the solutes desorb from the surfactant structures as they are solubilized in the free micelles. Naphthalene, which is strongly adsorbed on the silica surface in the absence of surfactant, is also desorbed as micelles are formed. Comparisons of the micellar solubilization effect as determined from solute desorption or direct micellar solubilization experiments display differences that may be attributed to the retention of some solutes on the adsorbed surfactant structures (hemimicelles or admicelles) in the presence of free micelles. It is shown that for all solutes studied the free energy of coadsorption is larger than the free energy of micellar solubilization.

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

“…[4] solute concentration, and k S the Setchenow constant. This coefficient is negligible when P mic is large (5). A plot of C s t is the total initial solute concentration and the index max the left-hand side versus m N gave a straight line, in agreement designates the maximum surfactant adsorption.…”

“…A small Tyndall effect was revealed {0.2 pH unit from the pH values stated above. The isotherm for that surfactant with Sorbsil C30 has been determined by a fade blue color, which suggested that a small fraction of titanium dioxide particles in the range of the primary previously at pH 3.6 and 6.5 (5). The data needed for the present discussion will be taken from that publication.…”

“…with Eq. [5]. The numerical value of the slope is equal to [4], the maximum concentration of solute coadsorbed can 83.3 for 1-naphthylamine.…”

“…The final value obtained in the be calculated if the two partition coefficients are known or molar scale is then P mic Å 830. A value of P mic Å 1940 has can be evaluated and if the maximum adsorbed surfactant been obtained before for NaphEtOH in CTAB micelles (5). is known.…”

“…The results will be compared to molecules which do not adsorb on the solid in the absence those obtained with the same solutes and surfactant on silica of surfactants. This phenomenon bears several names in the at pH 6.5 (5). literature: surface solubilization (1), adsolubilization (2), or coadsorption (3)(4)(5)(6).…”