Polyethylenimine-mica nanosheets/cellulose nanofibers stacked loose nanofiltration membrane for effective dye/salt separation

Dye recovery and desalination efficiency in textile wastewater treatment are of great significance, but the traditional treatment technologies cannot meet these two requirements simultaneously. In this study, a novel loose NF membrane was prepared by the assembly of PEI-modified mica (PEI-mica) and cellulose nanofibers (CNFs) on hydrolyzed polyacrylonitrile (HPAN) substrate via facile vacuum filtration. The combination of PEI-mica nanosheets and CNFs constructed a thin and loose “brick-mud” structure via electrostatic attraction and hydrogen bonding. The 2D nanochannels among the stacked PEI-mica nanosheets well-tailored by CNFs allowed the transport of water molecules and salt ions while resisting dye molecules. Due to the well-designed lamellar structure along with the excellent hydrophilicity, the PEI-mica/CNFs membrane possessed high water permeability (62.18 LMH/bar) and superior dye/salt separation efficiency, with outstanding dye retentions (i.e., Coomassie Brilliant Blue R250: 99.66 %, Congo Red: 98.89 %, and Evans Blue: 98.64 %) and low salt rejections (e.g., NaCl: 3.42 % and Na2SO4: 15.63 %). Besides, the composite membrane also showed good antifouling properties and operation stability, indicating its promising potential for practical textile wastewater treatment.