Benchmark C ₂ H ₄ /C ₃ H ₆ Separation in MOF–COF Bilayer Membranes via Interfacial Coordination Induced Sub‐Angstrom Channel Regulation

Abstract Olefins including ethylene (C 2 H 4 ) and propylene (C 3 H 6 ) 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 C 2 H 4 and C 3 H 6 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 C 3 H 6 /C 3 H 8 to C 2 H 4 /C 3 H 6 . 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 Zn 2+ 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 C 2 H 4 and C 3 H 6 , achieving a C 2 H 4 permeance of 405 GPU and an exceptional C 2 H 4 /C 3 H 6 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 cm 2 ) on polymer substrates.