Constructing substrate of low structural parameter by salt induction for high-performance TFC-FO membranes

Abstract

Forward osmosis (FO) is a promising membrane-based technology for water treatment and desalination. But, internal concentration polarization (ICP), a unique phenomenon in FO, generally leads to the sharp performance decline. In this study, a novel polyacrylonitrile (PAN) substrate with low polymer concentration (4 wt%) of the thin-film composite (TFC) membrane with a low membrane structural parameter (S) is developed with sodium chloride (NaCl) aqueous solution as the coagulation bath, and exhibits high performance for FO applications. The existence of NaCl in the coagulation bath not only affects the phase inversion process significantly, resulting in the formation of a thin substrate with finely tuned morphology structure, but also benefits the formation of a uniform and defect-free top polyamide (PA) layer. Effects of NaCl content in the coagulation bath on the morphology and intrinsic properties of resulting PAN substrates, the formed PA layer, as well as the morphology and FO performance of resulting TFC membranes, are investigated systematically. Moreover, an extended study on cellulose acetate (CA) substrate is also conducted to study the universality of this salt induction method to fabricate high-performance TFC membranes. Compared to the control TFC membrane, modified TFC membranes show much lower S parameters and superior separation performance with the higher water flux (324% increment) and lower reverse salt flux (58% reduction).