Simulations of Methane Adsorption and Diffusion within Alkoxy-Functionalized IRMOFs Exhibiting Severely Disordered Crystal Structures

Ordered structural models of alkoxy-functionalized isoreticular metal−organic frameworks (IRMOFs) were constructed by optimizing the symmetry and conformation of their flexible organic moieties. The selection of the initial model structures among the many chemically equivalent possibilities was performed by comparing their single-point energies using density functional theory (DFT) calculations. From these models, the adsorption and diffusion of methane within the porous hosts were simulated using grand canonical Monte Carlo (GCMC) computations and molecular dynamics (MD) simulations. The constriction of the pore dimensions by functionalization enhances the adsorption of methane at low to moderate pressures (<50 bar at 298 K), limits the saturation capacity of the materials, and inhibits adsorbate diffusion. The results obtained by this method are useful for scrutinizing the utility of functionalized IRMOFs for gas storage or separation applications.