Infrared study of the adsorption of fluoroalcohols on silica

Abstract

Infrared spectra have been recorded of ethanol, 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol adsorbed on silica at the solid/vapour interface and on silica immersed in carbon tetrachloride. The predominant surface–adsorbate interactions at ca. 306 K involved the formation of hydrogen bonds between surface silanol groups and hydroxy groups in adsorbed molecules. The strongest adsorption of this type occurred for single alcohol molecules adsorbed on to pairs of adjacent silanol groups. Isolated silanol groups acted as donors of hydrogen bonds, each to a single alcohol acceptor molecule. For ethanol, at high surface coverages lateral interactions between adjacent adsorbed ethanol molecules occurred and led to the build-up of aggregates of ethanol on the silica surface. Some chemisorption occurred for all three alcohols primarily through addition reactions at exposed strained siloxane groups.