Reticular Chemistry for Ionic Liquid-Functionalized Metal–Organic Frameworks with High Selectivity for CO<sub>2</sub>
Wen‐Long Xue, Lu Wang, Yu Kun Li, Hui Chen, Ke Xin Fu, Fan Zhang, Tao He, Yu Deng, Jian Rong Li, Chong‐Qing Wan
Abstract
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.