Infrared study of the adsorption of carboxylic acids on haematite and goethite immersed in carbon tetrachloride

Abstract

A novel infrared cell is described for the study of adsorption behaviour in situ at the solid/liquid interface. Spectra are reported of goethite immersed in solutions of succinic acid in carbon tetrachloride and of goethite and haematite in solutions of acetic, dodecanoic, dodecyl succinic and dodecenyl succinic acids. Chemisorptive interactions predominated and led to adsorbed carboxylate species primarily in the chelating bidentate configuration. The products of adsorption of substituted succinic acids also gave infrared bands characteristic of undissociated carboxylic acid groups. The ratio of COOH groups to carboxylate anions was greater for haematite than for goethite and greater for dodecenyl succinic acid than for dodecyl succinic acid. Alkyl chains close to the goethite or haematite surfaces hindered a mode of adsorption in which both carboxylic acid groups in an adsorbate molecule simultaneously interacted with a pair of adjacent chemisorption sites. The hindering effect was promoted when the hydrocarbon chain contained an alkenyl segment.