Computational investigation of multifunctional MOFs for adsorption and membrane-based separation of CF(4)/CH(4), CH(4)/H(2), CH(4)/N(2), and N(2)/H(2) mixtures

The ease of functionalization of metal–organic frameworks (MOFs) can unlock unprecedented opportunities for gas adsorption and separation applications as the functional groups can impart favorable/unfavorable regions/interactions for the desired/undesired adsorbates. In this study, the effects of the presence of multiple functional groups in MOFs on their CF(4)/CH(4), CH(4)/H(2), CH(4)/N(2), and N(2)/H(2) separation performances were computationally investigated combining grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The most promising adsorbents showing the best combinations of selectivity, working capacity, and regenerability were identified for each gas separation. 15, 13, and 16 out of the top 20 MOFs identified for the CH(4)/H(2), CH(4)/N(2), and N(2)/H(2) adsorption-based separation, respectively, were found to have –OCH(3) groups as one of the functional groups. The biggest improvements in CF(4)/CH(4), CH(4)/H(2), CH(4)/N(2), and N(2)/H(2) selectivities were found to be induced by the presence of –OCH(3)–OCH(3) groups in MOFs. For CH(4)/H(2) separation, MOFs with two and three functionalized linkers were the best adsorbent candidates while for N(2)/H(2) separation, all the top 20 materials involve two functional groups. Membrane performances of the MOFs were also studied for CH(4)/H(2) and CH(4)/N(2) separation and the results showed that MOFs having –F–NH(2) and –F–OCH(3) functional groups present the highest separation performances considering both the membrane selectivity and permeability.