Hydrogen Bonding Controls the Dynamics of Catechol Adsorbed on a TiO 2 (110) Surface

• Published in: Science (American Association for the Advancement of Science) 2010-05, Vol.328 (5980), p.882-884
• Main Authors: Li, Shao-Chun, Chu, Li-Na, Gong, Xue-Qing, Diebold, Ulrike
• Format: Article
• Language: English
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1188328

Direct studies of surface diffusion with instruments such as the scanning tunneling microscope (STM) have often focused on species on metal surfaces, but surface diffusion can play an important role for reactions on metal oxide surfaces. Li et al. (p. 882 ) used STM and density functional theory calculations to study how catechol (a benzene ring bearing two −OH groups) diffuses on the surface of the rutile phase of titanium dioxide. Both mobile and immobile species were observed on the time scale of minutes while making repeated STM scans. Hydrogen atom transfers between surface OH groups and the molecule changed the interaction energy between the molecule and the surface, and hence the barrier for diffusion. The diffusion barrier for an organic molecule on a hydroxylated metal oxide surface depends on hydrogen bond formation. Direct studies of how organic molecules diffuse on metal oxide surfaces can provide insights into catalysis and molecular assembly processes. We studied individual catechol molecules, C 6 H 4 (OH) 2 , on a rutile TiO 2 (110) surface with scanning tunneling microscopy. Surface hydroxyls enhanced the diffusivity of adsorbed catecholates. The capture and release of a proton caused individual molecules to switch between mobile and immobile states within a measurement period of minutes. Density functional theory calculations showed that the transfer of hydrogen from surface hydroxyls to the molecule and its interaction with surface hydroxyls substantially lowered the activation barrier for rotational motion across the surface. Hydrogen bonding can play an essential role in the initial stages of the dynamics of molecular assembly.