Facile fabrication of a positively charged nanofiltration membrane for heavy metal and dye removal

Positively charged membranes are essential for the removal of heavy metals from wastewater by nanofiltration (NF). A simple fabrication procedure for synthesizing a positively charged membrane with high permeance and high selectivity is needed to make this realistic. This work prepared a positively charged P84 NF membrane by chemical cross-linking of the asymmetric plain P84 membrane using hyperbranched polyethyleneimine (PEI). Instead of using organic solvent and thermal annealing, the cross-linking reaction occurred in mild conditions with a cross-linker concentration of 15 g L-1 and a cross-linking time of 20 h at ambient temperature in water. The modified membrane had increased surface hydrophilicity, surface roughness, and a positively charged surface. The resulting membrane had an excellent water flux of 43.2 L m(-2)h(-1)& nbsp;at 4 bar. The cross-linked P84 NF membrane showed high rejections of divalent heavy metals PbCl2, Ni(NO3)(2), ZnCl2, Cu(NO3)(2)& nbsp;with rejections of 99.0%, 96.7%, 96.2%, 99.8%, respectively, which outperforms the commercial NF270 membrane tested in the same conditions. Due to the high cross-linking of the active surface layer, the membrane was found to reject positively charged organic dyes almost completely: Victory blue B (VBB, 506.08 g mo1(-1)), methylene blue (MB, 319.85 g mo1(-1)), and negatively charged Congo red (CR, 696.66 g mo1(-1)). The convenient fabrication process could accelerate the progress of the positively charged NF membranes in potential applications of removing heavy metals and positively charged dyes from effluents in industries.

Automated summary

This study successfully synthesized a positively charged P84 NF membrane with high permeance and high selectivity using a simple fabrication method. The modified membrane exhibited excellent water flux and high rejections of heavy metals and positively charged dyes, making it suitable for potential applications in industrial wastewater treatment.