Hydration mechanisms of tungsten trioxide revealed by water adsorption isotherms and first-principles molecular dynamics simulations
Résumé
WO 3 is one of the most interesting materials for photocatalysis due to its optical absorption in the UV-Vis, good charge carriers transport and stability against photocorrosion. A detailed knowledge of the hydration state of WO 3 is indispensable to gain more precise mechanistic insights into its photocatalytic activity. To the best of our knowledge, the hydration process of WO 3 has been scarcely studied so far and only from a theoretical point of view, mostly by means of static density functional theory (DFT) calculations. Here, we use manometric gas sorption experiments combined with extensive ab initio molecular dynamics simulations to investigate the hydration mechanisms of WO3 at room temperature. We demonstrate that water adsorbs molecularly in a two-step mechanism: the first water sub-layer interacts with the undercoordinated surface tungsten atoms through electrostatic interactions, and, in a second step, a full layer is formed through hydrogen bonds established with the pre-adsorbed water molecules and with the under-coordinated surface oxygen atoms. The computed value of -90 kJ·mol-1 for the isosteric enthalpy of adsorption of the first water molecules is in excellent agreement with the experimental value estimated using the Clausius-Clapeyron approach from the experimental adsorption isotherms. The isosteric enthalpy of adsorption steadily decreases in absolute value when the surface coverage is increased to tend towards the enthalpy of condensation of water after three adsorption layers.
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23_Manuscript_WO3_hydration.pdf (2.56 Mo)
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23_WO3_hydration_SI.pdf (463.95 Ko)
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Licence : CC BY - Paternité
Licence : CC BY - Paternité
Licence : CC BY - Paternité