Molecular simulation of fluid adsorption in flexible nanoporous materials at multiple scales

Abstract : During my PhD, I used molecular simulation to study the adsorption and intrusion of fluids in flexible nanoporous materials. As of today, metal-organic frameworks (MOF) are the main example of this family of materials. I specifically worked with ZIF-8, a MOF built with zinc metallic centers and imidazolates linkers, organized in a sodalite topology. Using ab initio molecular dynamics I showed that nitrogen undergoes a reorganization inside the pores during adsorption; increasing the total adsorbed amount. I also showed that changes to the chemical nature of linkers allows to partially or completely remove this reorganization. On an other side, I used classical molecular dynamics and Monte Carlo simulations to study adsorption and intrusion of water in hydrophobic porous materials. These materials have possible applications in mechanical energy storage and dissipation. The intrusion pressure, as well as the presence and shape of an hysteresis loop, can be tuned by adding ions in the intrusion liquid. I showed that the liquid confined in ZIF-8 or in alumino-silicate nanotubes called imogolites is strongly structured; and that the water molecules dynamic slows down under confinement. The presence of ions almost does not modify the water structuration, but slows down dynamics even more, and makes the whole system more rigid. I also studied ions entry in ZIF-8 structure, and observed a clear difference between Li+ and Cl– both on a thermodynamic and kinetic point of view. Finally, I showed that it is necessary to take in account flexibility to correctly predict gas co-adsorption in frameworks that undergoes deformation (breathing, gate-opening, etc.) under adsorption. This is possible within the scope of Osmotic Framework Adsorbed Solution Theory (OFAST) for materials undergoing phase transition.
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Submitted on : Friday, July 12, 2019 - 11:57:00 AM
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Guillaume Fraux. Molecular simulation of fluid adsorption in flexible nanoporous materials at multiple scales. Chemical Sciences. PSL Research University; Chimie ParisTech, 2019. English. ⟨tel-02181661⟩

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