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One of the critical challenges faced by forward osmosis (FO) is the internal concentration polarization (ICP) during FO process, which can drastically reduce the effective osmotic driving force. In this work, silica nanoparticles were embedded in polyetherimide (PEI) nanofibrous support for making thin film nanocomposite (TFN) polyamide FO membranes to mitigate undesired ICP. The experimental results show that the pore size and porosity of the FO membrane substrate was significantly increased due to silica incorporation; the reason could be mainly attributed to the better heat-press resistance of the silica based nanofibrous substrates, leading to less substrate compaction and porosity reduction during the heat-press treatment. The FO membranes supported with such substrates demonstrated higher osmotic water flux, likely arising from the reduced structural parameter of the support layer. The current work showed that the FO membrane with the highest silica loading of 1.6 wt% in dope solution had the maximum substrate porosity (83%), the smallest structural parameter (~ 174 μm), and the most promising water flux, i.e., 42 L/m 2 h in the active layer facing the feed water orientation and 72 L/m 2 h in the active layer facing the draw solution orientation when 1.0 M NaCl draw solution and deionised feed water were applied. [ABSTRACT FROM AUTHOR]

One of the big challenges for forward osmosis (FO) practical application is the lack of high performance FO membranes. In this research, we successfully fabricated a novel thin film nanocomposite (TFN) FO membrane consisting of a polyetherimide (PEI) nanofibrous substrate reinforced by functionalized multi-walled carbon nanotubes (f-CNTs) and an ultrathin polyamide rejection layer. In addition to the superior inter-connected porous structure of nanofibrous substrate, the well-distributed f-CNTs in the nanofibers increased the substrate porosity by 18% and reduced membrane's structural parameter ( S value) by 30%, and significantly improved the substrate tensile modulus by 53%. The high mechanical strength provided by the embedded f-CNTs enabled us to further increase the substrate pore size and porosity in order to mitigate the internal concentration polarization (ICP). This was demonstrated by the high performance TFN-2 FO membrane with a structural parameter of 310 μm. Its water flux at 1.0 M NaCl draw solution (DS) was as high as 61 and 33 L/m 2 h in the active layer facing draw solution (AL-DS) and active layer facing feed water (AL-FW) orientations, respectively, indicating the success of the design strategy, i.e., improved membrane mechanical strength enables a further improvement of the membrane structure to mitigate the ICP. [ABSTRACT FROM AUTHOR]