Anti-scaling covalent organic framework membranes with custom-tailored nanochannels for efficient lithium extraction

Covalent organic framework membranes (COFMs) with well-defined nanochannels have infinite potential in efficient separation. However, unsuitable pore size and easily contaminated surface hamper the application of COFMs for ion separation. Herein, we report a custom-tailored nanochannels strategy for forming COF nanosheets (COFNs) with positively charged, narrowed and lithiophilic channels. The obtained COFNs can be easily assembled into free-defect and oriented COFMs via vacuum-assisted filtration method. Charged and narrowed channels augment entrance resistance of divalent cation, meanwhile, lithiophilic groups promote transport of Li+ in channels. Besides, positively charged surface disturbs the crystallization of scaling. Thus, the optimal COFM exhibited excellent water permeance of 32.1 L m−2 h−1 bar−1 and high Li+/Mg2+ separation factor of 30.2 in simulated salt-lake brine. After running in the gypsum solution, the anti-scaling COFMs showed low flux decline ratio (FDR) and the flux recovery ratio (FRR) was nearly 10% higher than NF90. This study may provide a facile regulation method for nanochannels and surface properties of COFMs, and the obtained membranes could be applied to efficient lithium extraction.