Carbodiimide-assisted zwitterionic modification of poly(piperazine amide) thin-film composite membrane for enhanced separation and anti-depositing performances to cationic/anionic dye aqueous solutions.

In this work, a novel method of carbodiimide-assisted zwitterionic modification was proposed and implemented to incorporate zwitterionic moieties onto poly(piperazine amide) membrane for improved water permeability and anti-depositing property, which are crucial for highly efficient nanofiltration of dye-contained effluents. Carboxyl groups of polyamide layer were firstly transferred into N-acylurea using excess l-ethyl-3-(3-(dimethylamino)propyl)-carbodiimide. Zwitterions were then incorporated through ring-opening reaction between tertiary amine groups of N-acylurea and 1, 4-butanesultone. Carbodiimide-assisted zwitterionic modification was verified by ATR-IR and XPS analyses and was found to not affect membrane pore size but significantly enhance membrane's permeation and anti-dye-deposition performances. Compared with those of virgin membrane, water permeabilities of the desired zwitterionic membrane to pure water, Congo red aqueous solution and Victoria blue B aqueous solution were higher by 42.9, 62.3 and 95.2 %, respectively, hydraulic resistances from irreversible deposition of Congo red and Victoria blue B molecules were dramatically lowered by 68.4 and 91.8 %, respectively. Furthermore, the perm-selectivity performance of the desired zwitterionic membrane in terms of molecular weight cut-off and pure water permeability was better than most of the reported zwitterionic membranes, and the separation and anti-depositing performances to both anionic and cationic dye aqueous solutions were better than commercial membrane NF270.