Stress Relief and Reactivity Loss of Hydrated Anatase (001) Surface

Dissociative and molecular water adsorption on the anatase (001) surface is studied in the context of state-of-the-art density functional theory in large supercells suited for adsorption studies at various water coverage ratios. At low coverage values below 1/4 ML, water adsorption remains dissociative and a network of hydrogen bonds between the so formed hydroxyl groups favors the formation of a ridge surface structure. The hydroxyl patterned (4 × 4) surface thus undergoes a (2 × 4) reconstruction that causes the relief of the large tensile stress measured in the unreconstructed surface along the direction orthogonal to the ridge. This phenomenology is accompanied by the loss of reactivity of the reconstructed surface with respect to the dissociative water adsorption that becomes molecular above 1/4 ML. We also show that the molecular adsorption on the terrace is weaker than the one on the ridge. The present water reconstruction model is discussed and compared to the well-known ADM model of the reconstructed anatase (001) surface in dry environment.