Diffuse Reflectance Fourier Transform Infrared Study of the Adsorption of Oleate/Oleic Acid onto Titania

Fourier transform infrared spectroscopy in diffuse reflectance mode is used to study the nature of the adsorbed species when rutile form titania is exposed to aqueous oleate/oleic acid over a range of pH values. Any of the oleic acid dimer, the monomer, or the anion may be adsorbed, depending on the oxide sample, in particular the incidence of surface Lewis acid sites. The results suggest that oleic acid monomer can be adsorbed by coordination as a σ-bonded ligand to Ti 4+ Lewis acid sites, via its carbonyl group oxygen. The oleic acid dimer appears to simultaneously coordinate to two adjacent Lewis sites via the hydroxyl oxygens. At pH 3 there is evidence that the adsorbed amphiphiles make two-point contact with the oxide surface via an interaction of the CH CH group with surface OH 2 + groups.