Sub-nanochannel induced by interlayer shifting in covalent organic framework membranes enables ultrahigh proton selectivity

Proton separation is critical for a variety of industrial processes, yet achieving high selectivity for protons over metal ions remains a significant challenge. Here, we report a covalent organic framework (COF) membrane that exhibits exceptional proton-metal ion separation efficiency. The COF membrane features unique sub-nanochannels induced by interlayer shifting, which is achieved via a controlled interfacial polymerization process. These sub-nanochannels provide an optimal size for proton transport while effectively excluding larger metal ions. Additionally, the positive surface charge of the membrane induces electrostatic repulsion toward metal ions and offers abundant hydrogen donors, further enhancing proton transfer. As a result, the membrane exhibited unprecedented selectivity factors for H + /Na + , H + /Sr 2+ , H + /Mg 2+ , H + /Al 3+ , H + /La 3+ , and H + /UO 2+ 2 , with values of 127, 4273, 4738, 1.3 × 10 4 , 1.36 × 10 6 , and 6107, respectively, surpassing most existing membranes by one to three orders of magnitude. Furthermore, we demonstrate its practical application for the deacidification of highly acidic (3 M HNO 3 ) spent nuclear fuel raffinate, where, within 24 h of continuous operation, the feed acidity decreased by nearly 50%, with no detectable leakage of radioactive metal ions across 30 diverse radioactive cations.