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[Display omitted] • Smart COF membranes were constructed via biomimetic nanochannel modulation. • Charged and switchable channels endowed COF membranes with high ion selectivity. • Pore size of photo-responsive COF membranes was controllable at angstrom level. • Photo-responsive COF membranes showed great potential in lithium extraction. Smart nanochannels can regulate ion transport behavior by external stimulus and display precise ion selectivity in biological membrane systems, but constructing artificial membranes with responsive and tunable channel remains a severe challenge. Herein, smart covalent organic framework (COF) membranes decorated with photo-responsive azobenzene derivatives (COF-Azo) were fabricated by a biomimetic nanochannel modulation (BNM) strategy, endowing membranes with charged and switchable sub-nanochannels. Under different wavelength of light, the smart COF-Azo membranes simultaneously exhibited outstanding mono/monovalent and mono/divalent ion selectivity (K+/Li+ ideal selectivity of 17.9 and Li+/Mg2+ ideal selectivity of 24.9) via closing and opening channels. The conversion of effective pore size at angstrom level is realized by photoisomerization of azobenzene. After several photoswitch cycles, the smart membranes still maintained K+/Li+ selectivity of 6.1 and Li+/Mg2+ selectivity of 20.7 in mixed salt solution, exhibiting great potentials in lithium extraction. This work may blaze a trail in constructing photo-responsive nanochannel membranes for energy-efficient ion separation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ion selective COFMs were constructed via custom-tailored nanochannels strategy. • Charged, narrowed and lithiophilic channels endowed COFMs with high selectivity. • Positively charged surface prevented scaling formation on the COFMs. • The anti-scaling COFMs showed great potential in 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. [ABSTRACT FROM AUTHOR]