Infrared study of the adsorption of hydrocarbons on rutile at the solid–vapour and solid–liquid interfaces

Abstract

The adsorption of n-heptane, toluene and 1,4-dimethylbenzene vapours on to the surface of rutile has been studied by infrared spectroscopy. Surface hydroxyl groups were perturbed to a lesser extent by weak interactions with physically adsorbed n-heptane molecules than by stronger hydrogen-bonding interactions with the aromatic nuclei of toluene or 1,4-dimethylbenzene. Hydroxyl groups responsible for an infrared band at 3410 cm^–1 in spectra of rutile were unaffected by the adsorption of hydrocarbons and are thought to be at sub-surface lattice sites. Two types of surface hydroxyl group were replaced by a chemisorbed oxidation product, possibly acetate anions, when rutile was exposed to 1,4-dimethylbenzene vapour.

Infrared spectra are reported of rutile immersed in the liquids n-heptane, toluene and 1,4-dimethylbenzene and mixtures of n-heptane + toluene and n-heptane + 1,4-dimethylbenzene. The perturbation of surface hydroxyl groups by the components of the liquid phases were monitored as a function of the composition of the hydrocarbon mixtures. Sub-surface hydroxyl groups remained unperturbed when rutile was immersed in the hydrocarbon liquids.