Water Confined in Mesoporous TiO2 Aerosols: Insights from NMR Experiments and Molecular Dynamics Simulations

The adsorption of water vapor in mesoporous TiO2 was studied by nuclear magnetic resonance (NMR) and multiscale molecular dynamics simulations. Three different water environments were distinguished and quantified: a first layer, where strongly bound water molecules exist at the inner surfaces; a second less structured layer but still with restricted mobility; and a bulk-like fraction of mobile water. The obtained NMR results can be explained in the framework of molecular dynamics simulations that give insight on the filling mechanisms in TiO2 nanoporous materials. For these highly hydrophilic materials, it is shown that adsorption isotherms may render a smaller effective pore size due to the presence of a layer of highly bound water. The synergistic combination of experimental NMR data and MD simulations renders a detailed analysis of the water dynamics inside the titania pore space.