Fabrication of highly permeable CS/NaAlg loose nanofiltration membrane by ionic crosslinking assisted layer-by-layer self-assembly for dye desalination

A loose nanofiltration (NF) membrane for dye desalination was prepared by ionic crosslinking assisted layer-by-layer self-assembly method. The natural chitosan (CS) and sodium alginate (NaAlg) were used as the cationic and anionic polyelectrolytes, respectively. CaCl2 was used as the ionic crosslinker based on the chelating ability of NaAlg and CS to Ca2+ ions. The structures, morphologies and surface charge properties of the assembly layers were characterized. In addition, the effects of self-assembly conditions and operation conditions on the filtration performances of composite membranes were evaluated systematically. The results indicate that the dye rejection of assembled membrane increases due to the crosslinking of Ca2+ ions. The resultant HPAN-(CS/NaAlg)3 membrane shows high rejections to dyes (98.8% for Congo red, 98.9% for Coomassie brilliant blue G-250, 98.5% for Direct black 38) and low rejections to inorganic salts. Moreover, HPAN-(CS/NaAlg)3 membrane exhibits high permeate flux (54.8 L·m−2·h−1·bar−1), good stability in continuous filtration and antifouling property.