Exploring Methane Storage Capacities of M2(BDC)2(DABCO) Sorbents: A Multiscale Computational Study

A promising solution for efficient methane (CH4) storage and transport is a metal–organic framework (MOF)-based sorbent. Hence, searching for potential MOFs like M2(BDC)2(DABCO) to enhance the CH4 storage capacity in both gravimetric and volumetric uptakes is essential. Herein, we systematically elucidate the adsorption of CH4 in M2(BDC)2(DABCO) or M(DABCO) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn) MOFs using multiscale simulations that combined grand canonical Monte Carlo simulation with van der Waals density functional (vdW-DF) calculation. We find that, in the M(DABCO) series, Mg(DABCO) has the highest total CH4 adsorption capacities, with mtot= 231.39 mg/g at 298 K, for gravimetric uptake, and Vtot= 231.43 cc(STP)/cc, for volumetric uptake. The effects of temperature, pressure, and metal substitution on enhancing CH4 storage are evaluated, and we predict that the volumetric CH4 storage capacity on M(DABCO) could meet the DOE target at temperatures of ca. 238 K–268 K and pressures of 35–100 bar. The interactions between CH4 and M(DABCO) are dominated by the vdW interactions, as shown by the vdW-DF calculations. The Mg, Mn, Fe, Co, and Ni substitutions in M(DABCO) result in a stronger interaction and thus, a higher CH4 storage capacity, at higher pressures for Mg, Mn, Ni, and Co and at lower pressures for Fe. This work may provide guidance for the rational design of CH4 storage in M2(BDC)2(DABCO) MOFs.