Mitigating internal concentration polarization in forward osmosis membranes via PSf-g-PHEMA amphiphilic graft copolymer-modified sublayer

A thin, porous, and hydrophilic sublayer is essential in the forward osmosis (FO) process to minimize the structural parameter (S), thereby reducing internal concentration polarization (ICP). In this study, the polysulfone (PSf) sublayer of the FO membrane is modified with an amphiphilic graft copolymer, poly(sulfone)- graft -poly(2-hydroxyethyl methacrylate) (PSf-g-PHEMA). The PHEMA with terminal alkyne functional groups is synthesized via atom transfer radical polymerization (ATRP) and subsequently grafted onto azide-functionalized PSf using click reaction. Sublayers are prepared through the phase inversion process by adding different concentrations of the PSf-g-PHEMA copolymer to the PSf casting solution. Different analyses reveal substantial enhancements in the properties of the copolymer-blended sublayer, including improved hydrophilicity, porosity, pure water permeability, and optimized morphology. These improvements are attributed to the hydrophilic segments of the graft copolymer, which influence the phase inversion rate. The membrane containing 10 wt.% PSf-g-PHEMA exhibited the highest water flux in both pressure-retarded osmosis (PRO, 34.5 LMH) and FO (19.4 LMH) modes, compared to the unmodified thin-film composite (TFC) membrane (5.9 LMH). This performance is associated with a significantly reduced structural parameter (S, 478 μm), indicating effective mitigation of ICP. Overall, these findings highlight the significant potential of amphiphilic graft copolymers to enhance the performance of TFC-FO membranes. • Poly(sulfone)- graft -poly(2-hydroxyethyl methacrylate) (PSf-g-PHEMA) established as functional additive • Integration of PSf-g-PHEMA yields optimized PSf-based sublayers for polyamide thin-film composite forward osmosis (FO) membranes • Amphiphilic PSf-g-PHEMA as membrane modifier enhances FO performance by reducing the structural parameter