Polymer‐in‐Cage Strategy for Pore Tuning of High‐Aspect Ratio ZIF Nanoplate: Toward Sub‐Micrometer‐Thick Large Area CO ₂ Separation Membranes

Mixed-matrix membranes (MMMs) offer a promising route for CO₂ separation, yet their potential is often limited by poor polymer-filler interfaces and challenges in integrating high-aspect-ratio fillers into scalable, defect-free thin-film composite (TFC) membranes. Here, we introduce a "polymer-in-cage" strategy that addresses these issues in a single casting step. A custom-synthesized comb-shaped copolymer (PZO) containing zinc-ion sites is designed to function dually as a mechanically robust matrix and an active pore-modulating agent for high-aspect-ratio ZIF-8 nanoplates (NZIF-8). The copolymer's Zn²⁺-acrylate sites electrostatically anchor into the ZIF-8 pore windows, constricting their flexible apertures to enhance molecular sieving. The resulting TFC membranes exhibit an exceptional CO₂/N₂ selectivity of 80 and a CO₂ permeance of 333 GPU. This performance stems from a dual enhancement, where polymer-induced pore tuning is amplified by the tortuous diffusion pathways created by the aligned nanoplates. Furthermore, the membranes demonstrate excellent operational durability under high-pressure, humid, and long-term conditions. By uniquely integrating polymer chemistry with MOF architecture, this scalable strategy offers a new design paradigm for fabricating next-generation membranes for CO₂ capture and other critical separations.