Nanocomposite substrates for controlling internal concentration polarization in forward osmosis membranes

Forward osmosis (FO) is an emerging membrane separation technology with many potential applications. The water flux performance of existing FO membranes is largely limited by the internal concentration polarization (ICP) of solutes in their porous substrates. The current study investigated the use of nanocomposite substrates for controlling ICP and thus improving FO water flux. Polysulfone-nanocomposite (PSfN) substrates were prepared via phase inversion by incorporating porous zeolite nanoparticles in polysulfone. The PSfN0.5 (with 0.5 wt% zeolite loading) substrate showed improved surface porosity and hydrophilicity. A thin film composite (TFC) polyamide active layer was prepared by interfacial polymerization on the PSfN0.5 substrate, and the resulting TFC-PFSN0.5 membrane showed significantly enhanced water permeability compared to the TFC membrane prepared on a conventional polysulfone substrate. Under identical testing conditions, the FO water flux of the TFC-PFSN0.5 membrane was more than doubled of that of the conventional TFC membrane. Using 2 M NaCl as draw solution (DS) and 0–0.01 M NaCl as feed solution (FS), PSfN0.5-TFC had an FO water flux as high as ∼80 LMH in the active layer facing DS (AL–DS) orientation and ∼40 LMH in the AL–FS orientation. Further analysis revealed that the incorporation of zeolite nanoparticles significantly reduced the substrate structural parameter (S=0.34 mm for PSfN0.5-TFC compared to 0.96 mm for TFC). The current study demonstrates for the first time the use of porous particles and nanocomposite substrates for controlling ICP in FO operation.