Counterion exchanged hydrophobic polyelectrolyte multilayer membrane for organic solvent nanofiltration

Abstract

Organic solvent nanofiltration is a promising separation technology for removing solute from an organic medium. However, the fabrication of organic solvent nanofiltration membranes with stable separation performance is still a challenge. Herein, a hydrophobic polyelectrolyte multilayer membrane was prepared through a layer-by-layer self-assembly and counterion exchange method. Poly(diallyl dimethyl ammonium chloride) (PDDA)/polyacrylic acid (PAA) multilayer was self-assembled on the surface of the hydrolyzed polyacrylonitrile substrate through electrostatic interaction. Simultaneously, calcium silicate hydrate (CSH) nanoparticles were in situ grown during the multilayer formation process due to the incorporation of precursor in polyelectrolyte solutions. Therefore, the surface roughness of the membrane was enhanced and the anti-swelling property of the polyelectrolyte multilayer was also improved. The hydrophilic [(PDDA/PAA-CSH)2.5]+Cl− membrane was then converted to the hydrophobic membrane through the counterion exchange between Cl− and perfluorooctanate (PFO−) ions. The obtained [(PDDA/PAA-CSH)2.5]+PFO− membrane has a water contact angle of 118°, which can be used to separate dyes from ethanol. Both the separation performance and stability of the polyelectrolyte multilayer membrane were improved through the in situ growth of calcium silicate hydrate nanoparticles and counterion exchange by perfluorooctanate ions. Therefore, this strategy may open a new avenue to prepare organic solvent nanofiltration membranes.