Computational design of novel highly connected COFs for CH4/H2 adsorption and separation

Abstract

Ten new highly connected cubic boronitrate (-B4N4O12-) base covalent organic frameworks (BN-COFs) were designed in the lta and aco topologies. These structures were optimized and characterized computationally using density functional theory (DFT) and molecular mechanics methods. The structural characterization reflects that these BN-COFs possess the appropriate structural parameters for CH4/H2 adsorption and separation, such as low density (0.52–1.28 g·cm−3), high pore porosity (22 %-72 %), appropriate pore limiting diameter (PLD, 2.45–6.71 Å) and the largest cavity diameter (LCD, 3.21–19.96 Å), large pore volume (0.15–1.37 cm3·g−1) and accessible surface area (332–3974 cm2·g−1). Grand canonical Monte Carlo (GCMC) simulations were conducted to investigated the adsorption and separation properties of CH4 and H2 in ten BN-COFs. The results indicate that the uptake capacity of methane and hydrogen in BN-COF-5, −9 and −10 has exceeded the targets set by the U.S. Department of Energy (DOE). Furthermore, the CH4/H2 selectivity of ten BN-COFs is comparable to that of typical porous materials. The outstanding CH4/H2 adsorption and separation properties of these BN-COFs can provide some references and inspirations for researchers to develop high-performance porous adsorbents in experimental studies.