Summary of directed computational approach based on the structure-performance relations

https://doi.org/10.1016/j.cej.2021.131574

“In this study, we screened 69,840 hypothetical COFs by using an efficient and structurally directed computational approach based on the structure-performance relations that we produced for experimentally synthesized COFs. Results showed that hypoCOF adsorbents outperform experimentally synthesized COFs in PSA (VSA) processes due to their high CO₂ selectivities, 6.13–742 (6.37–954), and large working capacities, 0.07–8.68 mol/kg (0.01–3.92 mol/kg). APSs of hypoCOFs were computed in the range of 0.43–3566 mol/kg and 0.05–3736 mol/kg, achieving almost six and two times larger upper limits than those of experimentally synthesized COFs at PSA and VSA conditions, respectively. DFT calculations on two hypoCOFs, which only differ in their linker fragments, showed that CO₂ and H₂ form van der Waals interactions with the linkers, whereas additional hydrogen bonds formed between CO₂ and linker substituents. The linker containing –OH substituents (linker2) form stronger hydrogen bonds with CO₂ than the linker with –CH₃ substituents attached (linker77), thus, higher Sads,CO2/H2 is observed for the hypoCOF constructed from –OH functionalized linker. We then examined 794 hypoCOF membranes and showed that all hypoCOFs surpass the Robeson’s upper bound due to their higher H₂ permeabilities (9×10⁵-4.5×10⁶ Barrer) and H₂/CO₂ selectivities (2.66–6.14) compared to those of polymer membranes. HypoCOFs outperformed experimentally synthesized COFs, zeolites, and MOFs as they achieve at least two times larger H₂/CO₂ membrane selectivities. Almost half of hypoCOF membranes was computed to have higher selectivity and permeability than the best experimental COF membrane, CCOF-2, reported in our previous work [27]. Results pointed out that hypoCOFs having bor- and pts-topologies with linker91 and linker92 tend to achieve very high adsorbent performances whereas unh- and sod-hypoCOFs with linker103 and linker94 were clear standouts among membranes. These results show that hypoCOFs are very promising adsorbents and membranes for CO₂ capture and H₂ purification. Considering the commercial availability of the linkers, synthesis of the promising hypoCOFs can lead to new, novel materials with high CO₂/H₂ separation performances.”