Tailoring Nanofiltration Membranes by Incorporating Zwitterionic Quaternary Ammonium Terpolymer to Enhance Performance

Designing nanofiltration membranes with unique characteristics and properties is an emerging trend for water treatment research. Herein, we introduced the unique example of the aliphatic diethylenetriamine-based nanofiltration membranes and tuned its selectivity by adding the terpolymer. To enhance the permeability of the salts while maintaining the rejection of the dye Eriochrome black T (EBT), a novel cationic/zwitterionic terpolymer of Diallyldimethylammonium chloride (DADMAC), 3-(N,N-diallyl-N-methylammonio)propanesulfonate (DAMAPS), and N,N-diallyldodecane-1,12-diamine (DADA) was rationally synthesized and in situ grafted via interfacial polymerization (IP) in the polyamide active layer of the membrane. The incorporation of poly-(DADMAC-co-DAMAPS-co-DADA) polymer into the diethylenetriamine polyamide active layer results in 5.8 times increase in water flux while still retaining an outstanding rejection rate of ~99.9 % for EBT. Furthermore, it exhibited enhanced salt permeability for NaCl, MgCl₂, Na₂SO₄, and MgSO₄. The grafted polymer increased the hydrophilicity of the membrane and strengthened stability for long-term working conditions. Thus, the aliphatic diethylenetriamine membranes have great potential for desalination, and their active layer can be tuned with the zwitterionic moieties to enhance the salt permeability and keep the EBT rejection higher than 99 %, which makes these membranes valuable for environmental and textile applications.