Aliphatic polyamide nanofilm with ordered nanostripe, synergistic pore size and charge density for the enhancement of cation sieving

Enhanced cation sieving selectivity is significant for polyamide (PA) nanofiltration membrane in terms of extracting lithium from Salt Lake brines, which enable to reduce production cost and operating energy consumption. Herein, an aliphatic PA nanofilm with ordered nanostripe was fabricated using a novel distorted and non-coplanar monomer, cyclopentane tetracarboxylic acid chloride (CPTC). Because of the fine-tuning of the dendrimer porous layer, the resultant aliphatic PA membrane revealed decreased thickness in separation layer, and an enhanced synergistic effect of size exclusion and Donnan equilibrium on mono-/divalent cation. Separation experiments indicated that a higher MgCl2 rejection (up to 98.36%) and a lower LiCl rejection (33.3%) were obtained, thus achieving a good cation selectivity (48.25 for Na+/Mg2+, 36.5 for Li+/Mg2+). This result was better compared with the full-aromatic and most of the literature reported positive charged PA membranes. Moreover, water flux of the CPTC–tris(2-aminoethyl) amine (TAEA) membrane with nanostripe structure (N-CPTC–TAEA) increased 3.98–4.74 times (for example, 135.9 ± 4.62 for 2000 ppm LiCl) that of the CPTC–TAEA membrane. Meanwhile, the N-CPTC–TAEA also exhibited a better antifouling property than that of the full-aromatic membrane. This study demonstrates that the N-CPTC–TAEA tends to be an alternative membrane material for cation separation.