In-situ construction of ionic ultramicroporous metal–organic frameworks for high-efficiency CO2/CH4 separation

The high-efficiency capture of CO 2 from biogas by adsorption is highly desirable, which, yet faces the challenges regards of the unsatisfactory adsorption efficiency, selectivity, and regeneration performance. Herein, ionic ultramicroporous metal organic frameworks (IUM-MOFs) with high CO 2 affinity are constructed by one-step in-situ coordination strategy and used for CO 2 /CH 4 separation. The phenoxylate anion-functionalized ionic liquid (FIL) serves as competitive ligands in the formation of IUM-MOFs. The oxyl group exhibits high affinity with CO 2 as the Lewis basic center, while the rigid counterion occupies the adsorption space of CH 4 in the cavities of IUM-MOFs, thus bringing about superior CO 2 adsorption capacity of 149 cm 3  g −1 (150% higher than that of Cu-BTC) and high IAST predicted selectivity with CH 4 of 22 under atmospheric condition. Mechanism analysis demonstrated that the formation of hydrogen bonds between CO 2 with coordinated IL and H 2 O and IL-enhanced polarity of MOFs benefit to the CO 2 adsorption. In addition, the IUM-MOFs could be facilely regenerated at 120 °C with favorable recycling stability. This work provides facile strategy for the rational design of IUM-MOFs and lays useful insights for structural tuning to promote their applications.