Reticular Chemistry for Ionic Liquid-Functionalized Metal–Organic Frameworks with High Selectivity for CO2

Carbon dioxide capture and separation are of great importance for cutting greenhouse gas emissions. A series of Zr(IV)-based MOF UiO-67-MIMS(x) (0 ≤ x ≤1) derived from mixed linkers 4,4′-biphenyl-dicarboxylate linker (BPDC) and its derivative bearing imidazolium sulfonate (BPDC-MIMS) at the 2-position were designed and synthesized. Their pore sizes and structures are well tuned by varying the x ratio of the two mixed linkers. Binary ionic liquid moieties (MIMS/salt) were furnished by subsequently incorporating the sodium salts within UiO-67-MIMS(x), engendering a series of ionic liquid-decorated MOF composites, namely, UiO-67-ILs-anion (anion = Cl–, ClO4–, BF4–, PF6–). The optimal pore size, the imidazolium sulfonate group with affinity sites to CO2, and various anions of ionic liquid moieties have a synergistic effect on the CO2 adsorption and separation. UiO-67-ILs-Cl ([Zr6O4(OH)4(BPDC-MIMS)1.5(BPDC)(4.5)]-NaCl) exhibited a high uptake of CO2 of 85.20 cm3/g (273 K and 1 atm), and its infinite dilution selectivity of CO2/N2 reached 36.56. All composites were characterized through powder X-ray diffraction (PXRD), N2 adsorption isotherms, CO2-selective adsorption study, FT-IR spectroscopy, energy dispersive X-ray (EDX) spectroscopy, and thermogravimetric analysis (TGA). The CO2 adsorption and selective roles of such MOF-based composites were systemically investigated by experimental and theoretical methods.