Healing Intercrystalline Defects of ZIF‐8 Membrane by Hydrophobic and Sterically Hindered Ionic Liquid for Humid Propylene/Propane Separation

Conventional post-synthetic intercrystalline defect-healing strategies for zeolitic imidazolate framework-8 (ZIF-8) membranes, such as secondary growth and polymer coating, can improve propylene/propane (C3H6/C3H8) selectivity but inevitably increase membrane thickness or occupy the intrinsic pores of ZIF-8, leading to compromised permeance. Moreover, the relatively poor water stability of ZIF-8 membranes under high humidity severely impedes their practical application. Herein, two hydrophobic and sterically hindered ionic liquids (HSH-ILs), BpyNTf2 and P6,6,6,14NTf2 are introduced to heal the intercrystalline defects of ZIF-8 membranes while preserving the intrinsic porosity of ZIF-8 and imparting humidity resistance. As a consequence, the P6,6,6,14NTf2@ZIF-8 membrane demonstrates a high C3H6 permeance of 174 GPU together with an outstanding C3H6/C3H8 selectivity of 101. Notably, owing to the protective barrier formed by HSH-IL, such excellent separation performance can be well reserved even after an aggressive humidity test. Experimental results and theoretical calculations reveal that the superior separation performance originates from the synergistic contribution of intrinsic pores of ZIF-8 and interfacial interactions between HSH-ILs and ZIF-8. This work opens a new avenue for constructing defect-free and humidity-resistant polycrystalline membranes toward challenging gas separation processes.