Tuning the CO2 selective adsorption performance in MOFs by incorporating functional groups on the isophthalate skeleton

By introducing functional groups into the isophthalate ligand to decorate the pore of the MOFs, gas adsorption and separation performance can be tunable. In this paper, two isostructural 2D Co-MOFs, [Co(5-MIA)(bpy)].H2O (1) and [Co(5-EIA)(bpy)].H2O (2) (5-H2MIA = 5-methoxyl-isophthalic acid; 5-H2EIA = 5-ethyoxyl-isophthalic acid; bpy = 4,4 '-bipyridine), with different functionalized pore surfaces and channel sizes were designed and constructed. The structures and performance of the two Co-MOFs were analyzed by SCXRD, PXRD, IR, TGA, and gas sorption (CO2, C2H2, CH4, CO, and N2). Attributed to the methoxyl of isophthalate skeleton, 1a (activated 1) shows enhanced CO2 uptake over other gases. In spite of decreased pore sizes (3.49 angstrom) compared with 2a (4.38 angstrom), the CO2 uptake of 1a (43.41 cm3 g-1) is larger than that of 2a (22.39 cm3 g-1) at 298 K and 100 kPa. Compound 1 incorporates methoxyl groups into the narrow channel, and exhibits the cooperative effect of CO2- preferential due to adsorbent-adsorbate coactions and size sieving. GCMC simulation has been used to explore the adsorption coactions of CO2 and 1, and the results confirmed that the methoxyl groups in the channel are the main binding sites of CO2. At ambient temperature and 100 kPa, the IAST selectivities of CO2/C2H2 (1:1), CO2/ CH4 (1:1), C2H2/CH4 (1:1), CO2/CO (1:2) and CO2/N2 (15:85) on 1a were 2.6, 39.3, 13.3, 282 and 1433, respectively. The easy activation and regeneration, excellent thermal and humidity stability, and good reusability, make 1a hopeful adsorbent for adsorption and separation of CO2.