Thin film composite forward-osmosis membranes with enhanced internal osmotic pressure for internal concentration polarization reduction

Abstract

• FO membranes were prepared by incorporating SPPO in substrate. • IOP was generated in the SPPO/PSf membranes. • The effects of IOP were demonstrated via structural parameter analysis. • ICP was mitigated in the SPPO/PSf membranes. • High water fluxes were demonstrated in FO seawater desalination. Thin-film composite (TFC) forward-osmosis (FO) membranes with enhanced internal osmotic pressure (IOP) were used to reduce internal concentration polarization in this study. These TFC membranes contained a selective polyamide layer deposited by interfacial polymerization on a support substrate cast from a polymer blend of polysulfone (PSf) and sulfonated poly(phenylene oxide) (SPPO). The immobilized counter ions (Na + ) in SPPO gave rise to an IOP which facilitated water transport in the AL–FS operating mode (i.e., the active layer is facing the feed solution, also referred to as the FO mode) but retarded water transport in the AL–DS operating mode (i.e., the active layer is facing the draw solution, also called as the pressure retarded osmosis (PRO) mode). An optimized TFC membrane could draw a water flux of 39 LMH (Lm −2 h −1 ) in the AL–FS mode, which is among the highest in the current literature; and 57 LMH in the AL–DS mode, which is comparable to other published works using deionized water as the feed and 2 M NaCl as the draw solution. The optimized SPPO/PSf TFC membrane also outperformed other published FO membranes in simulated seawater desalination. Extremely high water fluxes of 25 and 19 LMH could be obtained in the AL–DS and AL–FS modes respectively. The impressive high water flux in the AL–FS mode makes this membrane particularly suitable for FO operations where internal concentration polarization (ICP) and membrane fouling are major concerns.