Improved surface hydrophilicity and antifouling property of nanofiltration membrane by grafting NH2-functionalized silica nanoparticles

Organic fouling has been a major impediment for the widespread application of nanofiltration membranes because it could degrade the performance and shorten the service life of such membranes. In this study, the NH2-functionalized silica nanoparticles (NH2-SiO2 NPs) were grafted on the surface of commercial NF90 membrane to improve the hydrophilicity and antifouling property with the N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride coupled with the N-hydroxysuccinimide (EDC/NHS) to activate carboxyl groups on the membrane surface. The surface roughness (Ra) of this modified membrane decreased from value of 47.4nm of the pristine membrane to 43nm. The water contact angle of the modified membrane decreased from 48.4 degrees to 15 degrees, indicating the high hydrophilicity of the surface. Moreover, the EDC/NHS membrane showed good stability when it was exposed to the ruinous physical stress (2-min sonication). The optimized grafting conditions, including the SiO2 concentration (0.5wt%), the activation time of EDC/NHS (20min), and the reaction time of NH2-SiO2 NPs with membrane surface (12h), were obtained by a series of experiments. Under the antifouling test of 36hours with bovine serum albumin (BSA) and hexadecyltrimethylammonium bromide (CTAB) as foulants, the EDC/NHS membrane lost 42.1% and 49.6% of its initial flux, respectively, which is lower than that of the pristine membrane (52.2% and 68%, respectively). After cleaning with deionized water for 2hours, the EDC/NHS membrane also showed significant improvement of flux recovery ratio (92% and 87%, respectively) than did the pristine membrane (70.3% and 60%, respectively).