Exploration of the Long-Chain N-Alkanes Adsorption and Diffusion in the MOF-Type MIL-47 (V) Material by Combining Experimental and Molecular Simulation Tools
Résumé
The adsorption properties of linear long chain alkanes (from n-pentane to n-nonane) within the rigid MOF MIL-47 (V) have been explored by combining gravimetry measurements and molecular simulations. Both experimental absolute isotherms and enthalpies of adsorption for all n-alkanes were compared with those obtained by configurational bias grand canonical Monte Carlo simulations (CB-GCMC) based on two different force fields. From a fair agreement between experimental and simulated data, a further step consisted of investigating the microscopic adsorption mechanism in play to shed some light onto the preferential orientations and conformations of all investigated n-alkanes. Whereas the trans conformation is predominantly observed for all n-alkanes, the proportion of the n-alkane conformations lying parallel to the direction of the tunnel significantly increases with the chain length, emphasizing that the confinement effect is stronger for the longer chain n-alkanes. Finally, molecular dynamics simulations allowed us to emphasize that all n-alkanes follow a pathway along the direction of the tunnel, leading to a 1D type diffusion mechanism, the motions being mainly centered around the middle of the pores at low loading, whereas they are significantly shifted toward the pore wall when the alkane concentration increases.