Separation and anti-dye-deposition properties of polyamide thin-film composite membrane modified via surface tertiary amination followed by zwitterionic functionalization

This work focused on modification of polyamide based thin-film composite membrane via a novel strategy combining surface tertiary amination and zwitterionic functionalization for improved separation and anti-dye-deposition properties. Surface tertiary amination was conducted through grafting polyethyleneimine (PEI) onto the surface of base membrane at the sites of carboxylic groups activated by 1-ethyl-3-(3-dimethylamino-propyl)-carbodiimide. Zwitterionic functionalization was implemented through in situ ring-open reaction be-tween tertiary amine groups of grafted PEI molecules and 1, 4-butanesultone. It was found that grafting of PEI could enhance CaCl2/NaCl rejection ratio from 0.36 to 3.05 through reversal of surface charge at a sacrifice of pure water permeation coefficient from 9.7 to 8.6 l/m(2) h bar. The following incorporation of zwitterions under desired condition could resume pure water permeation coefficient to a higher value of 12.6 l/m(2) h bar and further enhance CaCl2/NaCl rejection ratio to 3.11. Furthermore, proper surface tertiary amination and zwit-terionic functionalization could even significantly improve membrane resistance to deposition by both cationic and anionic dyes. Membrane ?s water permeation coefficients to aqueous Congo red, Victoria blue B and meth-ylene blue solutions under steady state were enhanced by 72.5, 78.8 and 53.2%, respectively, and relative flux decline ratios were lowered by 80.5, 80.3 and 79.0%.