Structural modulation of UiO-66-NH2 metal-organic framework via interligands cross-linking: Cooperative effects of pore diameter and amide group on selective CO2 separation

Methane is regarded as a potential alternative energy and chemical raw material, and its separation from biogas by capturing CO 2 has become a hot issue of great significance and challenge. Taking the low partial pressure of CO 2 in biogas (~50% CO 2 and ~50% CH 4 ) into consideration, a facile pre-synthetic method was applied to endow UiO-66-NH 2 with high adsorption capacity and selectivity toward CO 2 , via interligands cross-linking of two-molecule 2-aminoterephthalic acids through amidation reaction. At 298 K, the CO 2 uptakes of UiO-66-DAM at 0.5 and 1 bar were 36.7 and 54.1 cm 3 ·g −1 respectively, which were 16.9% and 12.7% higher than those of UiO-66-NH 2 . Meanwhile, the CO 2 /CH 4 selectivity of UiO-66-DAM at 1 bar was 1.43 times that of unlinked framework. It could be speculatively attributed to the cooperative effects of amide functional groups and smaller pore diameter of UiO-66-DAM, which synergized with open Zr(IV) sites to enhance the binding affinity toward CO 2 . Moreover, the higher isosteric heats of adsorption for modified MOF at low loading also revealed the strong interactions between polar pore surfaces and guest CO 2 molecules. Along with the highly reversible adsorption-desorption behavior during recycling, the ligand-cross-linked UiO-66-DAM could be very promising for future practical applications of selective gas separation.