Adsorption potential energy of benzene on α-quartz

Abstract

A semiempirical calculation of the adsorption potential energy of benzene on α-quartz is presented, taking into account the dispersion and electrostatic contributions. Two crystal faces were analysed, those of the hexagonal prism and the primary rhombohedron. A rough calculation was first carried out considering the OH group as a whole, and then a more accurate one taking the hydrogen and the oxygen separately.

The section having the largest adsorption energy is that of the most hydroxylated face, the hexagonal prism. For this face, not taking into account any lateral interactions, an adsorption energy of – 19.0 kcal mol^–1 is obtained when the benzene molecule is parallel to the surface, and – 11.2 kcal mol^–1 when it is perpendicular. For the primary rhombohedron face, the energy values obtained are – 16.0 and – 17.4 kcal mol^–1, respectively, for the parallel and perpendicular orientations. These results show good agreement with the published experimental data.