Fabrication of nanofiltration membranes through the deposition of polyethyleneimine on SMA-polyethersulfone supports under acid catalysis for cationic dye/salt separation

Organic selective nanofiltration membranes, with high organic rejections and salt passages, have attracted extensive research attention, especially for dye/salt separations. In the present work, nanofiltration membranes with lower MWCO were prepared by depositing PEI aqueous on porous supports containing poly (styrene-maleic anhydride) (SMA), under the catalysis of sulfuric acid. The amines in PEI reacted with the anhydrides in SMA through electrophilic protonation–addition, forming a crosslinked dense layer. Under the optimal conditions, a nanofiltration membrane with a permeance of about 24.3 Lm−2h−1bar−1 and a MWCO of about 400 Da was obtained. The membrane was further evaluated by filtrating aqueous solutions of dye and/or salt. The rejections of cationic dyes (crystal violet and methylene blue) were as high as 99.9%. The rejection of Na2SO4 was only 3.6%. During the 24 h filtration process of the crystal violet and Na2SO4 mixed aqueous solution, the separation performance remained stable, indicating the PEI/SMA-PES nanofiltration membrane had excellent organic-water selectivity and organics-salts selectivity. The membrane may have good potential in positively charged dye desalination.