Infrared study of the adsorption of ethanoic acid and trifluoroethanoic acid on barium sulphate

Abstract

Infrared spectra are reported of ethanoic acid and trifluoroethanoic acid adsorbed on barium sulphate. Ethanoic acid was non-dissociatively adsorbed as a monomer, either by liganding to Ba²⁺ surface sites or by hydrogen-bond donation to sulphate ions, and as a dimer. Dissociative adsorption led to adsorbed ethanoate anions and the concomitant protonation of sulphate ions to give HSO^–₄. The enhanced Brønsted acidity and depleted Lewis basicity of trifluoroethanoic acid resulted in a much greater extent of dissociative adsorption at the expense of non-dissociative adsorption of acid monomer. The extent of dimer formation on the barium sulphate surface was similar for the two acids.