Two-dimensional lamellar stacking COF membrane with charge repulsion effect for ions separation

Billions of people are suffering from a shortage of clean water. Covalent organic frameworks (COFs) based membranes show promise in supplying clean water from saline waters due to their designable and controllable porous structures. However, the challenge lies in the rejection of salt ions during the pervaporation process, which is attributed to the relatively large pore size of COFs. Herein, we report the 2D BTCA-TAPB-COF membranes supported on porous ceramics for efficient desalination. The resulting BTCA-TAPB-COF composite membrane consists of nanometer-thick BTCA-TAPB-COF lamellas, which are grown in an oriented manner by suppressing the surface energy. Through pervaporation, the membrane exhibits nearly complete NaCl rejections and high fluxes when processing NaCl solutions at seawater levels, surpassing the reported polymeric membranes. Moreover, the BTCA-TAPB-COF composite membrane exhibits reliable stability for desalination. Effects of desalination methods and charge states of solutes on the exclusion performance are comparatively investigated using BTCA-TAPB-COF composite membrane, which suggest that the surface charge of BTCA-TAPB-COF contributes to high ion rejection via the Donnan exclusion effect.