Lewis acid-driven interlayer shifting in sub-nm 2D covalent organic framework membranes for hydrogen purification

Covalent organic framework (COF) membranes are promising for eco-friendly separations, but precise control of pore size at the angstrom level has been challenging, limiting their application in gas separation. This study introduces a pore redistribution method to reduce pore size to the sub-nanometer range in single-phase COF membranes. Using a Lewis acid (YbCF₃(SO₃)₃) as the catalyst, interlayer shifting in 2D COFs was observed, which accelerates imine formation and weakens interlayer stacking forces. The pore size was engineered from >1.0 to ~0.6 nm. The optimal membrane achieves a competitive H₂ permeance of 2253 gas permeation units (GPUs) and a high H₂/CO₂ selectivity of 21.6 in a binary equimolar gas test at room temperature, outperforming other one-phase COF membranes and exceeding the 2008 Robeson upper bound. This approach offers an effective strategy for engineering microporous materials for gas separation and other applications.