Adsorption of water and ammonia on TiO2-anatase cluster models

Density functional theory (DFT) calculations performed at B3LYP/6-31G∗∗ level are employed to study water and ammonia adsorption and dissociation on (1 0 1) and (0 0 1) TiO2 anatase surfaces both represented by totally fixed and partially relaxed Ti2O9H10 cluster models. PM3 semiempirical calculations were also conducted both on Ti2O9H10 and Ti9O33H30 clusters in order to assess the effect of cluster size. Following dissociation, the adsorption of H2O and NH3 by H-bonding on previously H2O and NH3 dissociated systems, respectively are also considered. It is found that the adsorption energies and geometries of water and ammonia molecules on (1 0 1) and (0 0 1) anatase cluster models depend on surface relaxation. The vibration frequency values are also calculated for the optimized geometries. The adsorption energies and vibration frequency values computed are compared with the available theoretical and experimental literature.