Comparison of the adsorption behaviour of solutions of dicarboxylic acids on carbon blacks

Abstract

Adsorption of aqueous and di-isopropyl ether solutions of a series of dicarboxylic acids (oxalic, malonic, succinic, glutaric, adipic, pimelic, and sebacic) by the carbon blacks Graphon, Spheron 6 (1000°), and Spheron 6 has been studied at 20°. For the aqueous systems, a pattern of adsorption has emerged with a regular increase of adsorption with increasing chain length at similar concentration, but with an alternation in adsorption at similar relative concentrations (x/x₀). The latter is probably due to the alternation in solubilities of the acids in water. For any given aqueous system, the fraction of the surface covered by acid is greatest for Graphon and least for Spheron 6, with that for Spheron 6 (1000°) being intermediate. The adsorption results in general fit a monolayer model with parallel orientation of the acids, and for many of the aqueous systems the adsorbed layer is a mixture of acid and water. The highest members of the series, pimelic and sebacic acids, show acid-monolayer coverage on Graphon (for aqueous systems) and, with increasing concentration, a possible multilayer adsorption. The di-isopropyl ether systems follow a pattern similar to the behaviour of monocarboxylic acids adorbed from organic solution by carbon blacks.