Free Radical Graft Copolymerization Strategy To Prepare Catechin-Modified Chitosan Loose Nanofiltration (NF) Membrane for Dye Desalination

In this study, a novel free radical graft copolymerization strategy was applied to prepare the catechin-modified chitosan loose nanofiltration (NF) membrane for dye desalination. First, catechin, the eco-friendly natural material, was grafted onto chitosan through a free radical reaction and self-cross-linking. Second, the catechin-grafted-chitosan conjugates were assembled onto the surface of the hydrolyzed polyacrylonitrile (HPAN) ultrafiltration (UF) membrane. Finally, the prepared membrane was characterized by FT-IR, XPS, SEM, AFM, electrokinetic analyzer, and contact angle goniometer. The results showed that the prepared membrane exhibited a high rejection for dyes (i.e., 99.6% for congo red, 98.7% for acid fuchsin, and 98.5% for crystal violet) and a low retention for inorganic salts (i.e., 4.8% for Na2SO4, 12.5% for NaCl, 15.8% for MgSO4, and 16.2% for MgCl2). The Na2SO4 rejection, especially, was 2–3 times lower than that of the reported loose NF membranes. Meanwhile, a high removal rate of 82% for NaCl with a dye loss rate of 10% was also observed in the constant-volume batch dye desalination process. Moreover, the membrane also possessed a good dye antifouling ability with a flux recovery ratio of 87.8% and an irreversible fouling ratio of 12.2%. Hence, this catechin-modified chitosan loose NF membrane shows a promising application for dye desalination.