Ultrathin ionic COF Membrane via Polyelectrolyte‐Mediated Assembly for Efficient CO2 Separation

Fabricating ultrathin covalent organic framework (COF) membranes toward high‐permeance molecular separations is highly desired yet challenging. Herein, a polyelectrolyte‐mediated assembly (PMA) strategy is developed to fabricate ultrathin ionic COF membrane for efficient CO2 separation. The PMA strategy allows a facile control over the assembly mode between polyethyleneimine (PEI) and TpPa‐SO3H, yielding PEI‐bridged ultra‐large COF nanosheets which are readily processed into COF membranes with thickness down to 8 nm. The resulting COF membranes exhibit a high CO2 permeances of 1371 GPU and CO2/N2 selectivity of 33 for stimulated flue gas. This PMA strategy may open up a new avenue to fabricating ultrathin 2D material membranes for diverse applications. A facile and straightforward polyelectrolyte‐mediated assembly strategy is developed, allowing the preparation of ultra‐large nanosheets composed of ionic covalant orgainc frameworks (COFs) and polyelectrolyte, and the fabrication of ultrathin COF membrane (down to 8 nm). The resulting membrane exhibits a CO2 permeance of 1371 GPU with CO2/N2 selectivity of 33, surpassing the state‐of‐the‐art COF membranes.