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Structuration and Dynamics of Interfacial Liquid Water at Hydrated γ‑Alumina Determined by ab Initio Molecular Simulations: Implications for Nanoparticle Stability

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journal contribution
posted on 12.12.2017, 00:00 by Romain Réocreux, Tao Jiang, Marcella Iannuzzi, Carine Michel, Philippe Sautet
Liquid water/solid interfaces are central in catalytic nanomaterials, from their preparation to their chemical stability under harsh catalytic conditions such as the hot aqueous medium used in biomass valorization. Here we report an ab initio molecular dynamics (AIMD) study of the γ-Al2O3 (110)/water interface using the most recent surface model available in the literature. The size of the simulation box and the duration of the AIMD simulation enables us to characterize the whole interface at the atomic scale. The simulation evidences a redistribution of protons within the chemisorbed water layer. The influence of γ-Al2O3 (110) is also important on the water molecules that are not bound to the surface: it is only above 10 Å that water recovers its bulk liquid behavior. The influence of alumina is structural, with preferred angular orientations for water molecules, and also dynamical. The translational self-diffusivity of water is diminished by up to 2 orders of magnitude, and the angular relaxation time increased up to a factor of 6. The influence of the interface on chemisorbed water molecules is also characterized with an infrared spectrum (fully simulated at the density functional theory level) that shows two distinct regions (3500 and 3200 cm–1) assigned to two different interfacial environments. This full characterization of the nanoscale interfacial zone highlights the specific physicochemical features of water that arise in contact with γ-Al2O3 and opens the door to an improved preparation of supported catalysts (from templating agents to protective coatings).