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-dimethylaminopropyl)-carbodiimide. Zwitterionic functionalization was implemented through in situ ring-open reaction between 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/m2 h bar. The following incorporation of zwitterions under desired condition could resume pure water permeation coefficient to a higher value of 12.6 l/m2 h bar and further enhance CaCl2/NaCl rejection ratio to 3.11. Furthermore, proper surface tertiary amination and zwitterionic 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 methylene 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%.