Fabrication of hollow-fiber nanofiltration membrane with negative-positive dual-charged separation layer to remove low concentration CuSO4

[Display omitted] •The LNF membrane with negative-positive dual-charged layer was prepared.•The relationship between microstructure of dual-charged layer and rejection was revealed.•The loose separation layer resulted in a high permeability (29.6 L m−2 h−1 bar−1).•The membrane exhibited excellent acid resistance and regeneration performance. To apply membrane separation technology to the treatment of low-concentration heavy metal ion wastewater, it is essential to fabricate a nanofiltration (NF) membrane with high flux and excellent rejection. In this work, organics (polyethyleneimine, gallic acid, trimesic acid, and polyacrylic acid) with different charges were successively introduced onto the outer surface of hollow-fiber NF membranes via chemical modification. That regulated the membrane surface charge under the premise of maintaining a loose separation layer. A negative-positive dual-charged membrane with a large mean effective pore size and long charged channels was successfully constructed. The evolution regularity of the microstructure of the separation layer was explored. The relation between a microstructure for a negative-positive dual-charged layer and low-concentration CuSO4 removal was interpreted. An effective removal (94.2%) was achieved while maintaining a high permeability (29.6 L m−2 h−1 bar−1). Also, the as-prepared membrane showed good acid resistance and an excellent anti-fouling property and regeneration ability after cleaning by sulfuric acid. The flux recovery ratio and rejection recovery ratio were as high as 96.9% and 99.2% respectively. This work provides a reference for fabricating high performance hollow-fiber NF membranes to effectively remove heavy metal ions with low-concentration.