Molecular modeling of the adsorption-induced expansion of graphene oxide frameworks with covalently bonded benzene-1,4-diboronic acid

Nanoporous activated carbons (AC) with specific surface areas close to the theoretical limits for graphene (2600 m²/g) and pores ~1 nm in width have interest for gas storage and separation. Generally, adsorbents are assumed rigid, even though they are formed by feeble quasi-2D structures resembling graphene flakes. In 2019, Schaeperkoetter et al. [1] observed swelling of graphene oxide frameworks (GOFs) upon the adsorption of methane and xenon under supercritical conditions, i.e., non-condensing. Here we show the results of extensive molecular dynamics simulations (MD) of methane and xenon in various models of GOF’s: (a) benzene-1,4-diboronic acid (DBA) molecules bonded covalently to graphene on both sides, (b) DBA bonded covalently on one side with van der Waals coupling to the other side, and (c) DBA in fluid phase interacting with various polar groups of graphene oxide. MD interaction parameters are based on ab initio B3LYP Density Functional Theory calculations. Our simulations show a monotonic increase of the interlayer spacing for both CH4 and Xe consistent with the experimental observations [1] only for model (a) with randomly oriented linkers.