Improved C₃H₆/C₃H₈ separation performance on ZIF-8 membranes through enhancing PDMS contact-dependent confinement effect

Polymer coating post-treatment strategy of the zeolitic imidazolate framework (ZIF) membranes offers a versatile and feasible opportunity to restrict the intrinsic flexibility of ZIF framework and improve their gas separation performance. Herein, two different coating methods (Vacuum-assisted drip coating (VADC) and Static drip coating (SDC)) are utilized to prepare PDMS/ZIF-8 composite membranes based on ZIF-8 membranes with different compactness (high, medium and low-quality membrane) for investigating the effect of the contact area between PDMS layer and ZIF-8 membrane on C₃H₆/C₃H₈ separation performance of PDMS/ZIF-8 composite membranes. The results reveal that the increase of the contact between PDMS layer and ZIF-8 membrane can enhance the contact confinement effect on the flexibility of ZIF-8 framework, resulting in a higher improvement of the separation performance for C₃H₆/C₃H₈ of PDMS/ZIF-8 composite membranes with pressure. The prepared composite membrane based on VADC method showed a significant improvement in C₃H₆/C₃H₈ separation factor (77–102) with slight increase in C₃H₆ permeance (about 10%) at feed pressure of 7 bar. Moreover, this facile vacuum-assisted drip strategy attenuated the impact of the quality of ZIF-8 membranes on fabrication reproducibility of the composite membranes, which can withstand high pressure. Therefore, this work advances ZIF-8 membrane moving forward to industrial C₃H₆/C₃H₈ separation.