Two-dimensional oxalamide based isostructural MOFs for CO2 capture

Metal-organic frameworks (MOFs), members of porous crystalline materials, have been investigated for CO2 capture and separation from various exhaust gas mixtures. An essential element to build new MOFs with improved CO2 capture and separation abilities is to understand the influence of functional groups on the surface of pores on gas adsorption properties. Oxalamide groups have two amide moieties that feature a strong affinity to CO2. In this study, three new isostructural Co(II), Zn(II), and Cd(II)-MOFs have been synthesized by using 3,3'-(oxalylbis(a-zanediyl))dibenzoic acid (3-OADAH2) ligand which has a CO2-philic oxalamide group. To the best of our knowledge 3,3'-(oxalylbis(azanediyl))dibenzoic acid (3-OADAH2) was used as a linker for the first time. X-ray diffraction analysis shows that the MOFs possess two-dimensional (2D) structures and the layers interact with each other through hydrogen bonds. Co-, Zn-, and Cd-3-OADA exhibit an excellent CO2 adsorption capacity of 8.87 wt% (45.15 cm3/g), 8.40 wt% (42.76 cm3/g), and 7.93 wt% (40.37 cm3/g) at 273 K and 3.98 wt% (20.27 cm3/g), 4.74 wt% (24.15 cm3/g), 3.68 wt% (18.72 cm3/g) at 298 K under 1 bar with isosteric heat of adsorption values (Qst) of about 34, 25, and 33 kJ/mol, respectively. This work opens a new opportunity for the development of functionalized 2D-MOFs with high CO2 capture capacity.