Modification of polyamide nanofiltration membrane with ultra-high multivalent cations rejections and mono-/divalent cation selectivity

• Published in: Desalination Vol. 527; p. 115553
• Main Authors: Hu, Ping, Yuan, Bingbing, Niu, Q. Jason, Chen, Kuo, Xu, Zewen, Tian, Bizhuo, Zhang, Xiaozhuan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2022
• Subjects: Dual-functional acyl chloride; High mono-/divalent cation selectivity; Nanofiltration membrane; Organic phase additive; Ultrahigh multivalent cations rejections; Nanofiltration membrane; Dual-functional acyl chloride; Ultrahigh multivalent cations rejections; High mono-/divalent cation selectivity; Organic phase additive
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/j.desal.2022.115553

Due to their inherent negatively charged surface and large intra-membrane pore, the typical polyamide nanofiltration membranes possess the inferior retentions against Ca2+/Mg2+ and undesired mono-/divalent cation selectivity. Here, a novel dual-functional acyl chloride monomer comprising two protected amino groups, 3,5-bis-(sulfinylamino)benzoyl chloride (AB2), is designed and used as organic phase additive that enables simultaneous regulation of the surface charge and pore structure of polyamide (PA) selective layer. Both structure characterizations and simulations confirm that AB2 additive significantly reduces surface negative charges, surface carboxyl density, surface roughness, thickness and mean pore size of the- separation layer, which sharpens pore size distribution, strengthens electrostatic repulsion to cations and enhances water molecule transport. As a result, the optimal PIP-TMC/AB2 membrane shows the remarkably improved CaCl2/MgCl2 rejections (above 99.0%) and mono-/divalent cation selectivity, together with a preferable permeate flux (135.3 ± 3.12 LMH), surpassing most commercial and advanced NF membranes. Moreover, its multivalent cations removal capability and Mg2+/Li+ separation performance retain outstanding in highly concentrated feed solution, suggesting it has enormous potential for water softening and lithium recovery from brine. [Display omitted] •3,5-bis(sulfinylamino)benzoyl chloride (AB2) is used as novel organic phase additive.•Corporation of AB2 enables simultaneous regulation of surface charge and pore structure of PA layer.•The optimal membrane exhibits ultrahigh multivalent cations rejections and mono−/divalent cation selectivity.•The role of AB2 in affecting PA layer structure and properties is elucidated.