Using molecular simulation to characterise metal-organic frameworks and judge their performance as adsorbents

Porous metal-organic frameworks (MOFs) have recently gained much attention as promising materials for gas adsorption. These materials are generated in a directed-assembly process from corner units and linker molecules. As a result of the building block approach, these materials offer the possibility to tune host / guest interactions and therefore to tailor them rationally for specific adsorption separation or storage tasks. In this paper, molecular simulations are used to study methane adsorption in isoreticular metal organic frameworks (IRMOFs). The simulations revealed three distinct regimes: at low loading, the amount adsorbed is proportional to the heat of adsorption, at medium loading to the accessible surface area and at high loading to the free volume. A detailed analysis of adsorption in interpenetrated structures revealed that interpenetration leads to larger surface areas and stronger sorbate - framework interactions but also to lower free volumes, higher framework densities and smaller pores all of which can have a negative impact on the adsorption performance.