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Substrate construction is considered as the most effective approach to alleviate the internal concentration polarization (ICP) effect, and therefore achieves the excellent performance of resultant thin-film composite (TFC) membrane in forward osmosis (FO) process. In this work, a well-aligned nanofiber substrate was prepared and employed for constructing the high-performance TFC-FO membrane for the first time. The physicochemical properties of the substrate, the micro-structure of polyamide layer and the separation performance of resultant TFC-FO membranes were systematically investigated. Taking advantages of the larger pore size and the better pore interconnectivity of the well-aligned nanofiber substrate, the resultant TFC-FO membrane achieves the best water fluxes of 50.7 and 62.9 LMH, accompanied with the ultralow reverse salt flux in FO and PRO modes, using deionized water feed solution and 1 M NaCl aqueous draw solution. This work may provide a new orientation in developing high-performance TFC membranes. Image 1 • Aligned nanofiber substrate with slit-shape pore structure was facilely prepared. • TFC membrane with aligned nanofiber substrate was reported for the first time. • Aligned nanofiber substrate alleviates internal concentration polarization effect. • TFC membrane with aligned nanofiber substrate shows excellent FO performance. [ABSTRACT FROM AUTHOR]

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). Image 1 • Substrates with low ICP were fabricated using salt-containing coagulation bath. • Modified substrates exhibit higher porosity, smaller thickness and large pore size. • TFC membranes with a modified substrate have rougher and thicker PA layers. • Modified TFC membrane possesses much higher water flux and lower reverse salt flux. • Modified TFC membrane has significantly lower structural parameter. [ABSTRACT FROM AUTHOR]