Abstract
We report a new type of alkaline-stable hollow-fiber reverse osmosis (RO) membrane with an outside-in configuration that was established via adsorption of positively charged poly(vinyl alcohol) copolymers containing a small amount of quaternary ammonium moieties. Anionic sulfonated poly(arylene ether sulfone nitrile) hollow-fiber membranes were utilized as a substrate upon which the cationic copolymer layer was self-organized via electrostatic interaction. While the adsorption of the low-charge copolymer on the membrane support proceeded in a Layer-by-Layer (LbL) fashion, it was found that the adsorbed amount by one immersion step was enough to form a defect-free separation layer with a thickness of around 20 nm after cross-linking of vinyl alcohol units with glutaraldehyde. The resultant hollow-fiber membrane showed excellent desalination performances (NaCl rejection of 98.3% at 5 bar and 1500 mg/L), which is comparable with commercial low-pressure polyamide RO membranes, as well as good alkaline resistance. The separation performance could be restored by repeating the LbL treatment after alkaline degradation. Such features of LbL membranes may contribute to extending RO membrane lifetimes.
Highlights
Reverse osmosis (RO) is a widely accepted desalination process
We examined a poly(vinyl alcohol-co-diallyldimethylammonium chloride) (CPVA) as a low-charge cationic polyelectrolyte for fabricating a separation layer adsorbed onto the anionic outer surface of hollow-fiber RO membrane
The zeta potentials of membrane materials investigated in this study were evaluated using polymeric films made from polyphenylene oxide (PPO), SPN-20, and XCPVA formed on an SPN-20 film
Summary
Reverse osmosis (RO) is a widely accepted desalination process. According to the forecast by Global Water Intelligence’s DesalData, the worldwide operating RO plant capacity reached 58.5 Mm3/day in 2020 and is expected to reach 82.1 Mm3/day in 2026. Liu et al [11] fabricated a poly(ethersulfone) (PES) hollow-fiber membrane and coated PAH and PSS on the inner surface of the membrane followed by cross-linking of PAH layer with glutaraldehyde. In their works, ionic strength and pH of polyelectrolyte aqueous solutions were carefully controlled and high NaCl concentration (typically 0.5–1.0 M) was maintained. We examined a poly(vinyl alcohol-co-diallyldimethylammonium chloride) (CPVA) as a low-charge cationic polyelectrolyte for fabricating a separation layer adsorbed onto the anionic outer surface of hollow-fiber RO membrane. The membrane had a separation layer comprised of sulfonated poly(arylene ether sulfone nitrile) containing benzonitrile moieties (SPN-20), which was coated on a polyphenylene oxide (PPO) hollow-fiber support.
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