Formamide adsorption over the TiO2 (110) surface: a theoretical study

The adsorption of monomeric formamide over the rutile TiO2 (110) surface has been studied by way of density functional theory. At a coverage of one formamide per two surface repeat units, there is very little difference in stability between molecular and dissociative adsorption configurations. At larger coverages, however, dissociative adsorption in a manner analogous to that observed for carboxylic acid becomes favoured. Stable adsorption modes for the initial steps of a formic acid-like decomposition route are also studied. In the presence of an oxygen vacancy, dissociatively adsorbed formamide bonds with either its N (or O) atom above the oxygen vacancy while the other atom (N or O) coordinates to a five-fold coordinated surface titanium atom. Both modes of adsorption are however found to be isoenergetic. Results provide a possible explanation for the experimentally observed nitriding of the TiO2 surface post adsorption. Density of States analyses indicated that the nature of interaction is mainly covalent with large degree of hybridisation between the formamide orbitals and surface states.