A novel positively charged composite nanofiltration membrane based on polyethyleneimine with a tunable active layer structure developed via interfacial polymerization

A novel positively charged composite nanofiltration (NF) membrane with tunable active layer structure was successfully developed via interfacial polymerization on a polysulfone (PSF) ultrafiltration (UF) membrane surface, using polyethyleneimine (PEI) as the monomer of the aqueous phase, and a mixture of isophthaloyl dichloride (IPC) and tri-mesoyl chloride (TMC) as the monomer of the organic phase. Interestingly, a synergetic effect of the mass ratio of IPC and TMC was observed on the pore size and the structure of the active layer of the resultant polyamide (PA)/polysulfone (PSF) composite NF membrane. The rejection (R) to the inorganic electrolytes increased with the mass ratio of IPC to TMC, while the permeate flux (F) escalated up to a 1:1 mixing ratio of IPC to TMC and dropped at higher mixing ratios. The rejection to different inorganic electrolytes decreased in the order of ZnCl2, MgCl2, CaCl2, CuCl2, MgSO4, NaCl, and Na2SO4. At ambient temperature and 0.4 MPa, the optimized membrane demonstrated R and F to 1 g L-1 MgCl2 aqueous solution as 98.1% and 27.6 L m(-2) h(-1), respectively. Its rejection to various dyes reduced significantly in the order of cationic red X-GTL (100%), rhodamine B (94.2%), cationic gold yellow X-GL (93.5%), and brilliant blue KN-R (43.9%), in agreement with the decrease in the molecular weight (M-w) and the overall charges of the dye.