Benchmark C2H4/C3H6 Separation in MOF-COF Bilayer Membranes via Interfacial Coordination Induced Sub-Angstrom Channel Regulation.

Olefins including ethylene (C2H4) and propylene (C3H6) are pivotal raw materials in the chemical industry, and methanol-to-olefin (MTO) process provides a sustainable strategy to replace conventional petroleum-based methods for the olefin production. The purification of olefin mixture is an essential part in the MTO process where membrane technology has emerged as a high-efficiency and energy-saving approach. However, it remains a critical challenge to achieve precise sieving of C2H4 and C3H6 due to their similar molecular size. Herein, we report an interfacial coordination induced sub-angstrom channel regulation strategy and achieve unprecedented cut-off shift of ZIF-8 from C3H6/C3H8 to C2H4/C3H6. Ionic covalent organic framework with crystalline structure and high-density sulfonate groups was used as growth template for ZIF-8 membrane. The coordination between sulfonate groups and Zn2+ ions induced lattice contraction of ZIF-8 framework, which is confirmed by XRD patterns and molecular dynamic simulations. The resulting membranes demonstrate a distinct cut-off between C2H4 and C3H6, achieving a C2H4 permeance of 405 GPU and an exceptional C2H4/C3H6 selectivity of 45, surpassing the separation performance of all reported membranes. Finally, we demonstrate the excellent scalability of this strategy by fabricating large area flat sheet membrane (>500 cm2) on polymer substrates.