High-performance support-free molecular layer-by-layer assembled forward osmosis membrane incorporated with graphene oxide

Forward osmosis (FO) membranes generally have a thin-film composite (TFC) structure comprising an ultrafiltration (UF)-grade support layer and a polyamide (PA) active layer. However, the lack of high-performance membranes limits FO. To improve the FO performance, internal concentration polarization (ICP) should be controlled to reduce the water flux within the support layer. In this study, a novel support-free molecular layer-by-layer (SF-mLbL) technique using a microfiltration (MF)-grade support layer for minimum ICP was applied to produce a robust and uniform active layer, even on large pores of the support layer. Based on the location of graphene oxide (GO) nanoparticles, thin-film nanocomposite (TFN) and thin-film nanocomposite-interlayer (TFNi) membranes were fabricated. Among these, the TFNi membrane with the highest performance contained 0.7 wt% GO nanoparticles and was stacked in 15 cycles. The 0.7 wt%-15 cycles TFNi membrane showed high water flux (87.18 ± 0.15 LMH) and low reverse salt flux (5.06 ± 0.11 gMH) when deionized (DI) water and 0.5 M NaCl solution were used as feed and draw solutions, respectively, in FO mode. This study demonstrates that the SF-mLbL technique is suitable for manufacturing high-performance FO membranes.