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

ABSTRACT Mixed‐matrix membranes (MMMs) offer a promising route for CO ₂ 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 Zn ²⁺ ‐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 CO ₂ /N ₂ selectivity of 80 and a CO ₂ 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 CO ₂ capture and other critical separations.