Fig. 5: Highly selective Na⁺/Li⁺ sieving.

a–c Control experiments. a, b Concentration of Na⁺ and Li⁺ in the permeate in response to permeation time, showing the low Na⁺/Li⁺ selectivity of AAO substrate (a) and the LDH/AAO composite membrane (b). c To confirm the absence of contamination, we also used DI water as the feed solution, and found no Na⁺ or Li⁺ contamination. d–f Permeation of Na⁺ and Li⁺ through the membrane when the feed solution contains Na⁺ and Li⁺ with concentrations of 0.001 M (d), 0.01 M (e), and 0.1 M (f) for each ion. g Summarized permeation rate for the tested binary mixtures of various concentrations, consistently showing the high Na⁺/Li⁺ selectivity. h Permeation of various cations through the membrane when the feed solution contains all five cations, each having a concentration of 0.1 M. i Permeation rate summarized from the data in (h), showing the robust selectivity in the solution with complex composition. Error bars in all cases represent standard deviation of the data from at least three individual experiments.