Adsorption of organic molecules on titanium dioxide (rutile) surface

Abstract

Adsorption isotherms of organic molecules, n-BuOH, n-BuCl and n-C₇H₁₆ have been measured on rutile samples having a controlled number of surface hydroxyl groups. The number of irreversibly adsorbed organic molecules decreased almost linearly with increasing surface hydroxyl group content of the sample. The hydroxyl groups on the rutile surface inhibit the irreversible adsorption of n-BuCl and n-C₇H₁₆, but allow only n-BuOH to be adsorbed irreversibly in appreciable amounts. From the results of infrared spectra and gas chromatographic analysis, it was evident that the irreversible adsorption of n-BuOH occurs on the dehydroxylated rutile surface through the mechanism of dissociation and/or of coordination to the surface Ti⁴⁺ ions, and on the hydroxylated surface through such reactions as substitution for molecular water and esterification with acidic surface hydroxy groups. The number of water molecules substituted by n-BuOH was estimated to be 1.255 molecules nm^–2. Non-polar n-C₇H₁₆ molecules and polar n-BuCl molecules were physisorbed on the rutile surface. The greater amount of n-BuCl adsorbed was interpreted in terms of the additional interaction between the dipole of n-BuCl and the electrostatic field of the rutile surface.