Nanofiltration Membranes Based on Rigid Star Amphiphiles

Rigid star amphiphiles (RSAs) of nanoscale dimension were synthesized and used to fabricate a new generation of nanofiltration (NF) membranes. NF membranes were prepared by direct percolation of methanol solutions of the RSAs through an asymmetric polyethersulfone (PES) support film that had been previously conditioned with methanol and cross-linked polyvinyl alcohol (PES-MeOH-PVA support). The resulting RSA membranes (RSAMs) have been shown to exhibit significantly enhanced water permeability while maintaining high rejection of water contaminants compared to commercial NF membranes. The RSAMs were characterized with the goal of elucidating the structural changes brought about by deposition of RSA. Characterization techniques used included attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrometry, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), confocal microscopy, Rutherford backscattering spectrometry (RBS), and gas adsorption/desorption analyses. Results suggest that the RSAs produce a uniform, ultrathin active layer atop the PES-MeOH-PVA support after lining its nanopores with sizes similar to those of the RSAs. Such active layer constitution was found crucial for rejecting organic contaminants and achieving high water flux. These findings encourage further exploration of NF membrane preparation by molecular deposition as an attractive approach for constructing ultrathin membrane active layers to remove challenging contaminants with high water permeability.