Ion-binding ameliorates the organic solvents nanofiltration performance of poly (butyl acrylamide-co-divinylbenzene) composites

•Poly (butyl acrylamide-co-divinylbenzene) nanofiltration membrane was synthesized.•The toplayer regularly distributed oxygen and nitrogen groups to anchor metal ions.•Fe-binding treatment enhanced the permeance and dye rejection in organic solvents.•Changes of the void size and the charge density in the toplayer were disclosed. A new nanofiltration composite membrane poly (butyl acrylamide-co-divinylbenzene) (poly-TaDb) was synthesized via a facile photopolymerization on polyetherimide using the monomers of n-tert-butyl acrylamide and divinylbenzene, and evaluated the separation performance in organic solutions. The unique poly-TaDb toplayer has a feature of branch structure containing regularly distributed oxygen and nitrogen groups that work as the interacting sites with metal ions (Fe3+, Zn2+, and Cu2+), as reflected by the characterizations of ATR-FTIR, XPS, AFM, etc. Without the metal ion treatment, the optimal poly-TaDb membrane shows the permeance of 31, 17, 20.4 L m−2h−1 MPa−1 respectively for organic solutions of tetrahydrofuran (THF), methanol (MeOH) and acetonitrile (ACN), with the rejection rates higher than 90% toward EB dye (879.8 g.mol−1). After interacting with these metal ions, the obtained Fe-binding poly-TaDb membranes possess higher permeance, with the THF, MeOH, and ACN permeance enhanced respectively to 113, 35, and 24.2 L m−2h−1 MPa−1, meanwhile maintaining high dye rejection rate. While the Cu- and Zn-binding membranes show much higher permeance but lower dye rejection rate. Density functional theory (DFT) calculations disclose that the void size of the toplayer network increases in the order of: the pristine (11.40 Å)