Adsorption at the solid-liquid interface. Part 4.—Adsorption of ethanol, n-octanol and n-dodecanol on defined rutile surfaces from binary liquid mixtures with p-xylene and n-heptane

Abstract

The adsorption on characterized surfaces of pure rutile of three aliphatic alcohols (ethanol, n-octanol and n-dodecanol) from solutions in p-xylene and n-heptane has been studied at 25°. Dependence of the adsorption on the alcohol chain length, chemical nature of the solvent and the presence of molecular water on the surface is demonstrated. The relative importance of the adsorption process of each of the various interactions involved, both in bulk solution and at the surface, are discussed. In addition to the more specific effects associated with hydrogen bonding, the interaction between the aromatic solvent and the hydroxyl groups leads to competitive adsorption, the magnitude of which depends on the fraction of the surface covered by molecular water. The aliphatic solvent competes with the alcohol for the non-hydroxylated regions and this is also related to the water coverage. Under all conditions the adsorption of octanol is the lowest of the three alcohols. Absence of appropriate thermodynamic data prevents a quantitative discussion of these effects.