Positively charged nanofiltration membranes hold great potential in Li⁺/Mg²⁺ separation, but their application in alkaline solutions, such as alkaline salt-lake brines has not been reported. Herein, inspired by the arginine's unique structure and biological function, we explore superstrong basic triaminoguanidine (TG) molecule as aqueous monomer to fabricate positively charged polyamide nanofiltration membranes for Li⁺/Mg²⁺ separation. With the Li⁺/Mg²⁺ mass ratios of 1:50 and 1:120, at pH 9.6, the separation factors (S_Li,Mg) of membranes reach 31.8 and 20.9. Meanwhile, at pH 5.6, the S_Li,Mg are 46.4 and 36.4, which are the ever-reported highest value and such high S_Li,Mg can be well retained in the pH range of 5.6–8.6. The superior Li⁺/Mg²⁺ selectivity stems from the superhigh protonation capacity of guanidine groups in a broad pH range.

带正电荷的纳滤膜在Li ⁺ /Mg ²⁺分离中具有巨大的潜力，但它们在碱性溶液中的应用，如碱性盐湖卤水尚未见报道。^{在此，受精氨酸独特结构和生物学功能的启发，我们探索超强碱性三氨基胍（TG）分子作为水性单体，制备用于Li +} /Mg ²⁺分离的带正电荷的聚酰胺纳滤膜。在Li ⁺ /Mg ²⁺质量比为1:50 和1:120 时，在pH 9.6 时，膜的分离因子（S _Li,Mg）分别达到31.8 和20.9。同时，在 pH 5.6 时，S _Li,Mg分别为 46.4 和 36.4，这是有报道的最高值，如此高的 S _Li、Mg在 5.6-8.6 的 pH 范围内可以很好地保留。优异的 Li ⁺ /Mg ²⁺选择性源于胍基在宽 pH 范围内的超高质子化能力。