High-performance loose nanofiltration membrane prepared with assembly of covalently cross-linked polyethyleneimine-based polyelectrolytes for textile wastewater treatment

Conventional nanofiltration membrane with high rejections to both dyes and inorganic salts are not suitable for the treatment of the textile wastewater. Herein, novel loose nanofiltration membranes were fabricated by the assembly of polyethyleneimine (PEI) and phosphorylated PEI (PEI-PO3Na) coupled with glutaraldehyde crosslinking. The PEI-based polyelectrolytes with branched structures and plentiful amine crosslinking sites enabled the formation of a highly permeable and robust selective layer. Meanwhile, the introduced phosphonate groups endowed the membrane with anti-fouling and anti-scaling properties owing to their surface hydrophilicity and chelation ability. By varying the molecular weight of PEI-PO3Na, the surface properties, pore size, and selective layer thickness and corresponding performances of the resultant PEI-PO3Na/PEI membranes can be successfully manipulated. The PEI-PO3Na 10 k/PEI membrane showed a high permeability (24.2 LMH/bar), high Victoria blue BO (99.5%) but low NaCl rejection (10.1%), demonstrating the best dye/salt fractionation performance. While PEI-PO3Na 70 k/PEI membrane exhibited the highest chroma and chemical oxygen demand (COD) removal rates, and the best anti-fouling ability for the textile wastewater treatment. The PEI-PO3Na/PEI membrane also exhibited good stability in various pH, and relatively low scaling propensity. This work provides a facile and convenient method for fabricating high-performance loose NF membranes for the practical textile wastewater treatment.