Solid/Solution Interface Equilibria for Aromatic Molecules Adsorbed from Non-aromatic Media: Part 2.—Aromatic Carboxylic Acids

Abstract

Data have been obtained for benzoic acid, 1-naphthoic acid and 2-naphthoic acid adsorption on the carbon blacks Graphon and Spheron 6, and on the oxides Alcoa C73O, Alon C, titanium dioxide and Cab-O-Sil using some or all of the solvents cyclohexane, carbon tetrachloride and cyclohexanone. Individual isotherms were calculated from the composite adsorption isotherms by well-established methods, thus enabling an assessment of the nature of the adsorbed phase. For the carbon blacks and some of the oxide adsorbents, the results are consistent with an adsorbed phase confined to a monolayer with a flat orientation of aromatic molecules; on the more polar oxide adsorbents however there is evidence of perpendicular orientation of the aromatic molecules in some cases, as well as of multilayer adsorption. Thermodynamic quantities for adsorption of the aromatic acids on the carbon blacks, AHa, AGa and ASa are calculated, and an attempt is made to correlate the trends observed with plausible adsorption models as well as with the nature of interactions at the interface.