Zhan, Zi-Ming, et al. Industrial & Engineering Chemistry Research 60.39 (2021): 14297-14306.
Challenge: Conventional polyamide nanofiltration (NF) membranes exhibit a trade-off among their water permeability, divalent ion rejection (softening), and antifouling properties, which significantly restricts their applications in water desalination.
Solution: A solution is to surface-graft polyquaternium-7 (PQ7), a cationic copolymer of dimethyl diallyl ammonium chloride and acrylamide, onto polyamide NF membranes. Simply grafting PQ7 onto polyamide NF membranes took advantage of its unique chemical structure and improved multiple performance.
Key Results:
· Electrostatic Repulsion: Positive charges of quaternary ammonium groups on PQ7 improved the electrostatic repulsion of divalent cations (Ca2+, Mg2+).
· Surface Modification: The surface hydrophilicity and roughness were enhanced by grafting of PQ7, while the membrane thickness was not changed.
· Economical Process: Simple grafting process using a cheap modifier (PQ7).
· Substantial Increase in Permeability: Water flux increased 66% (from 47.8 to 79.6 L m-2 h-1 at 5 bar).
· Superior Ion Rejection: Rejection of divalent ions reached exceptionally high levels due to enhanced positive surface charge.
· Excellent Antifouling Performance: PQ7-grafted membranes demonstrated superior flux recovery after fouling, and strong resistance to both organic foulants (sodium alginate) and protein foulants (bovine serum albumin).
Li, Jian, et al. Journal of Membrane Science 486 (2015): 89-96.