Theoretical Investigations of CO(2) and CH(4) Sorption in an Interpenetrated Diamondoid Metal–Organic Material

[Image: see text] Grand canonical Monte Carlo (GCMC) simulations of CO(2) and CH(4) sorption and separation were performed in dia-7i-1-Co, a metal–organic material (MOM) consisting of a 7-fold interpenetrated net of Co(2+) ions coordinated to 4-(2-(4-pyridyl)ethenyl)benzoate linkers. This MOM shows high affinity toward CH(4) at low loading due to the presence of narrow, close fitting, one-dimensional hydrophobic channels—this makes the MOM relevant for applications in low-pressure methane storage. The calculated CO(2) and CH(4) sorption isotherms and isosteric heat of adsorption, Q(st), values in dia-7i-1-Co are in good agreement with the corresponding experimental results for all state points considered. The experimental initial Q(st) value for CH(4) in dia-7i-1-Co is currently the highest of reported MOM materials, and this was further validated by the simulations performed herein. The simulations predict relatively constant Q(st) values for CO(2) and CH(4) sorption across all loadings in dia-7i-1-Co, consistent with the one type of binding site identified for the respective sorbate molecules in this MOM. Examination of the three-dimensional histogram showing the sites of CO(2) and CH(4) sorption in dia-7i-1-Co confirmed this finding. Inspection of the modeled structure revealed that the sorbate molecules form a strong interaction with the organic linkers within the constricted hydrophobic channels. Ideal adsorbed solution theory (IAST) calculations and GCMC binary mixture simulations predict that the selectivity of CO(2) over CH(4) in dia-7i-1-Co is quite low, which is a direct consequence of the MOM’s high affinity toward both CO(2) and CH(4) as well as the nonspecific mechanism shown here. This study provides theoretical insights into the effects of pore size on CO(2) and CH(4) sorption in porous MOMs and its effect upon selectivity, including postulating design strategies to distinguish between sorbates of similar size and hydrophobicity.