We have applied a combination of experimental and theoretical methods to study carboxylic acid (R-COOH) adsorption on TiO₂(110), and in particular to identify the interactions between the dissociated carboxylate (R-COO) and hydroxyl species. Carboxylates are common species present on the surface during photo-catalytic reactions on TiO₂. Earlier experimental results[1] suggested that the dissociative adsorption of trimethylacetic acid leads to a special configuration where the H atom is situated between two bridging oxygen (O_B) atoms while the carboxylate group forms a bridged species by attaching to two Ti cations. We characterized the dissociative adsorption configurations of these species using density functional theory (DFT), including the strength of the interaction between the OH group and the adjacent carboxylate through the nature of the OH and carboxylate molecular orbitals. We modeled the transfer of an H atom from one O_B to another O_B, and the stability of the shared-O_B configuration. Finally, theoretical STM images based on the model were generated. The theoretical findings provide evidence that the exact location of the dissociated H atom in relation to trimethylacetate cannot be determined from scanning tunneling microscopy (STM), and the H atom is also silent to high-resolution electron energy loss spectroscopy (HREELS)[1].

This work was supported by the Office of Basic Energy Sciences of the Department of Energy (DOE) at the Pacific Northwest National Laboratory (PNNL), and partially performed at the Environmental Molecular Science Laboratory, a DOE national user facility.  PNNL is operated by Battelle for the Department of Energy.