Computational simulation study on adsorption and separation of CH4/H2 in five higher-valency covalent organic frameworks

Abstract

The density functional theory (DFT) calculation and molecular simulation were implemented to investigate the structural characteristics and the adsorption/separation properties of CH4/H2 on five borophosphonate based higher-valency covalent organic frameworks (BP-COFs). The computed results reveal that five BP-COFs possess the low density, high void fraction, suitable pore size and accessible surface area for CH4 and H2. The grand canonical Monte Carlo (GCMC) simulations indicate that the CH4 uptake capacity is higher than H2 in all five BP-COFs at 298 K and BP-COF-1 and BP-COF-4 possess the better capacity for separating CH4 form CH4/H2 mixture with low CH4 partial pressure. The centroid density distribution profiles display that the preferable sites for CH4 and H2 are both located at the corners formed by the linear ligands and the hexahedron B4P4O12 clusters. This work may provide some inspiration for further exploring higher-valency COFs as gas adsorption/separation media.