Zeolitic imidazolate frameworks-based porous liquids with low viscosity for CO₂ and toluene uptakes

Porous liquids (PLs) as a novel class of materials combine the permanent porosity of microporous solids, the rapid mass transfer of liquids, and fluidity, thus exhibiting extraordinary promise for gas capture and separation. However, the practical application of PLs was severely restricted by their undesirable relative high viscosity and melting temperature. In this work, the symmetric dicationic ionic liquids [C₆BIm₂][NTf₂]₂ was synthesized as a steric hindrance solvent to construct a type of low viscosity zeolitic imidazolate frameworks (ZIFs)-based PLs. Specifically, the ZIF-67-PLs-2 (i.e., ZIF-67 loading of 2.0% in PLs) presented a low viscosity with 543.4 mPa·S at 25 °C, which was about 20 times lower than that of type III PLs reported previously. Meanwhile, ZIF-67-PLs showed long-term stability even over 180 days and broke the fluidity limitation down to −64 °C, broadening the work conditions. Moreover, ZIF-67-PLs-10 (i.e., ZIF-67 loading of 10.0% in PLs) achieved 55 times CO₂ and 7 times toluene adsorption capacity more than those of the corresponding pure DILs, respectively. Remarkably, the fascinating features of ZIF-67-PLs including lower viscosity, wide liquid range and higher adsorption pave a new way for the optimal design of novel PLs towards gas uptake and separation.