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

Abstract

Methane is regarded as a potential alternative energy and chemical raw material, and its separation from biogas by capturing CO2 has become a hot issue of great significance and challenge. Taking the low partial pressure of CO2 in biogas (~50% CO2 and ~50% CH4) into consideration, a facile pre-synthetic method was applied to endow UiO-66-NH2 with high adsorption capacity and selectivity toward CO2, via interligands cross-linking of two-molecule 2-aminoterephthalic acids through amidation reaction. At 298 K, the CO2 uptakes of UiO-66-DAM at 0.5 and 1 bar were 36.7 and 54.1 cm3·g−1 respectively, which were 16.9% and 12.7% higher than those of UiO-66-NH2. Meanwhile, the CO2/CH4 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 CO2. Moreover, the higher isosteric heats of adsorption for modified MOF at low loading also revealed the strong interactions between polar pore surfaces and guest CO2 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.