Fabrication of novel poly(m-phenylene isophthalamide) hollow fiber nanofiltration membrane for effective removal of trace amount perfluorooctane sulfonate from water

This study investigated the separation performance of a hollow fiber nanofiltration membrane, which was fabricated from poly(m-phenylene isophthalamide) (PMIA) using a dry-jet wet spinning technology, for sustainable water recovery from water containing trace amount of perfluorooctane sulfonate (PFOS) that was a persistent organic pollutant commonly existed in water. SEM spectra indicated that the cross section of the hollow fiber membrane had an asymmetrical structure that consisted of a dense outer surface acting as a selectively layer, a spongy-like transition layer, and finger-like microvoids close to the inner surface. The average pore size and molecular weight cut-off, which were estimated using the solute rejection method, were 0.404 nm and 904 Da, respectively. The PFOS rejection experiments were carried out at the trans-membrane pressures ranging from 4×105 Pa to 1.0×106 Pa and PFOS concentrations from 50 μg/L to 500 μg/L. In all cases, the PFOS rejections were found to be increased as the PFOS concentration increased. The impact of the pH value and Ca2+ concentration of the feed solution on the PFOS rejections was studied in detail. The PFOS rejections improved from 91.17% to 97.49% with an increase in pH from 3.2 to 9.5 at 4×105 Pa. An increase of Ca2+ concentration from 0.1 mM to 2 mM enhanced PFOS rejection from 97.10% to 99.40% at a trans-membrane pressure of 4×105 Pa. The sorption/desorption experiments indicated that the amount of PFOS adsorbed on the membrane surface was five times higher in the presence of Ca2+ (2 mM). AFM experiments also demonstrated that the membrane surface was rough with the addition of Ca2+. Hence, the presence of Ca2+ enhanced the PFOS adsorption in the membrane surface and caused more pore blockage of the membrane. As such, the declination in the water flux and augmentation in the PFOS rejection were observed.