Anisotropy in Conformation and Dynamics of a Glycolate Ion Near the Surface of a TiO2 Rutile Crystal Between Its {001} and {110} Planes: A Molecular Dynamics Study

A molecular dynamics simulation was conducted to elucidate the conformation and dynamics of a glycolate ion (CH2(OH)COO-) at the surface of a TiO2 rutile crystal. The simulation was performed for the {001} and {110} planes of the crystal. The results indicate that, for both planes, the conformation and dynamics of the ion are strongly dominated by a layered structure of water on the surface. The simulation suggests that the ion binds to the surface more stably on the {110} plane than on the {001} plane, and that the stable conformation of the ion at the surface differs between the planes: on the {110} plane the carboxyl group of the ion is preferentially oriented toward the surface, whereas on the {001} plane it is oriented toward liquid water. These simulation results are compared with the growth shapes of rutile crystals synthesized in the presence of glycolic acid, and the role of glycolate ions in controlling the morphology of rutile crystals is discussed.