Coadsorption of Naphthalene Derivatives and Cetyltrimethylammonium Bromide on Alumina/Water, Titanium Dioxide/Water, and Silica/Water Interfaces
✍ Scribed by P. Favoriti; V. Monticone; C. Treiner
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 135 KB
- Volume
- 179
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
scribe the partitioning of the solutes between the adsorbed The adsorption of cetyltrimethylamonium bromide at silica/wasurfactant structures and the aqueous solutions, much as in ter, alumina/water, and titanium dioxide/water interfaces has the classical case of micellar solubilization. Comparison bebeen determined at pH values for which these hydrophilic surfaces tween the partition constants in the two types of aggregate are all negatively charged. Then the coadsorption of 2(2-naphthyl) systems has shown that in the case of phenol (17) or 2ethanol and 1-napthylamine onto the surfactant aggregates was naphthol (4) the coadsorption effect is larger than the micelinvestigated both below and above the critical micelle concentralar solubilization. For molecules which do not dissociate into tion (cmc). The solute uptake from the aqueous solution increases ions with pH changes such as alcohols, the two partition with surfactant surface coverage up to the cmc and decreases coefficients are identical within experimental error (18).
above the cmc as the result of free micelle formation and preferential micellar solubilization. Solute partition coefficients were deter-
The silica surface is negatively charged above a pH value mined both for the coadsorption and the micellar solubilization of about 3. As it is well known, increasing the pH increases effects. Within experimental uncertainty, the coadsorption partithe number of negative sites on the silica surface and theretion coefficient for each solute is independent of the solid substrate fore increases the amount of adsorbed cationic surfactants. employed. It is solely a function of the surfactant adsorption and We have shown that the partition coefficient of an alcohol is of the neutral solute properties. The coadsorption partition coeffiindependent upon pH changes because of the proportionality cient is equal to the micellar solubilization constant for the alcohol, between the increase of adsorbed surfactant and that of but a ratio of about 2 in favor of the coadsorption constant is coadsorbed solute. The same behavior was observed upon found for the amine. The possible origin of this effect is discussed.
increasing the ionic strength of the solution (18).