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), [Bpy][NTf₂] and [P₆,₆,₆,₁₄][NTf₂] 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 [P₆,₆,₆,₁₄][NTf₂]@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.