Revisiting Water Adsorption on TiO₂ and ZnO Surfaces: An SCC-DFTB Molecular Dynamics Study

Metal oxides (MOs) are the key materials in applications of biomedicine industrial technologies due to their versatile features. Knowing their possible toxicity level is crucial given some specific environments, particularly in water. We have learned that their reactivity almost depends on the electronic structure on the surface of the MOs. Thus, a detailed understanding of the electronic structure on the surface and its reactivity processes is useful for determining the toxicity in MOs and defining good descriptive parameters. We simulated the interaction of ZnO and TiO₂ slab models with water and checked their geometric and electronic structure changes from the bulk of the material to the water interface. To this end, we used the density functional tight binding theory coupled with finite temperature molecular dynamics. We have observed the interaction of water with the MO surface in terms of electronic and geometric parameters for several conditions, such as temperature, hydrogenated or clean, and exposed surface. In doing so, we provide molecular-level insights into topographical and electronic processes on MO surfaces besides finding critical points on the surface that can explain the initialization of dissolution processes. Thus, we reveal information about potential toxicity descriptors in a systematic analysis approach.