Adsorption of water and induced pore pressures in nanopores
Résumé
Many nanoporous solids (e.g. activated carbons, zeolites, MOFs) can exhibit non-monotonic deformation upon adsorption, alternating between contraction and expansion stages according to the thermodynamic conditions and pore sizes. The case of water is particularly interesting, not only for its importance in many industrial applications and natural processes, but also because the adsorptive behaviour of this latter is complex and presents varied mechanisms. This study aims at characterising the adsorption-induced pore pressure of water in nanoscopic slit pores by molecular non-local density functional theory (DFT). The DFT is coupled with the statistical associative fluid theory for potential of variable range (SAFT-VR) which is highly accurate for the modelling of the bulk phase and equilibrium thermodynamic properties of water. This SAFT-DFT coupling has already been applied to methane confined in graphitic slit-like nanopores. While retaining the accuracy of molecular simulations at pore scale, the model has a very low computational cost that allowed obtaining highly resolved pore pressure maps as a function of both pore width and thermodynamic conditions.
In this work, several configurations are explored for confined water by changing both the thermodynamic conditions and the pore sizes. For instance, the capillary condensation and evaporation are investigated with the theoretical model in micro- and mesopores. The adsorption hysteresis gives rise to a pressure hysteresis for which consequences on the mechanical behaviour are investigated. The influence of the surfaces activation on water adsorption and pore pressure is also explored.