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

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.