Oxalamide-Functionalized Metal Organic Frameworks for CO Adsorption.

Metal-organic frameworks (MOFs) have received great attention in recent years as potential adsorbents for CO capture due to their unique properties. However, the high cost and their tedious synthesis procedures impede their industrial application. A series of new CO-philic oxalamide-functionalized MOFs have been solvothermally synthesized: {[Zn(μ-OATA)(HO)(DMF)]·5/2HO·5DMF} (Zn-OATA), {[NH(CH)][Cd(μ-HOATA)]·HO·DMF} (Cd-OATA), and {[Co(μ-OATA)(HO)(DMF)]·2HO·3DMF} (Co-OATA) (HOATA = ,'-bis(3,5-dicarboxyphenyl)oxalamide). In Zn-OATA, the [Zn(CO)] SBUs are connected by OATA ligands into a 3D framework with 4-connected NbO topology. In Cd-OATA, two anionic frameworks with a dia topology interpenetrated each other to form a porous structure. In Co-OATA, [Co(CO)] units are linked by four OATA to form a 3D framework with binodal 4,4-connected 4·8 PtS-type topology. Very interestingly, Cu-OATA can be prepared from Zn-OATA by a facile metal ions exchange procedure without damaging the structure while the CO adsorption ability can be largely enhanced when Zn(II) metal ions are exchanged to Cu(II). These new MOFs possess channels decorated by the CO-philic oxalamide groups and accessible open metal sites, suitable for highly selective CO adsorption. Cu-OATA exhibits a significant CO adsorption capacity of 25.35 wt % (138.85 cm/g) at 273 K and 9.84 wt % (50.08 cm/g) at 298 K under 1 bar with isosteric heat of adsorption () of about 25 kJ/mol. Cu-OATA presents a very high selectivity of 5.5 for CO/CH and 43.8 for CO/N separation at 0.1 bar, 298 K. Cd-OATA exhibits a CO sorption isotherm with hysteresis that can be originated from structural rearrangements. Cd-OATA adsorbs CO up to 11.90 wt % (60.58 cm/g) at 273 K and 2.26 wt % (11.40 cm/g) at 298 K under 1 bar. Moreover, these new MOFs exhibit high stability in various organic solvents, water, and acidic or basic media. The present work opens a new opportunity in the development of improved and cost-effective MOF adsorbents for highly efficient CO capture.