Development of zwitterion-functionalized graphene oxide/polyethersulfone nanocomposite membrane and fouling evaluation using solutes of varying charges

This study explores the functionalization of polyethersulfone (PES) ultrafiltration (UF) membranes using zwitterion-functionalized graphene oxide (GO) and assesses their interactions with solutes of different charges, both neutral and anionic. Initially, PES nanocomposite membranes were synthesized, incorporating varying dosages (ranging from 0-1 % (w/w)) of glycine-functionalized graphene oxide (Gly/GO) and diglycine-functionalized graphene oxide (diGly/GO) through a direct blending method. The physicochemical properties, including hydrophilicity, surface morphology, and porosity of these membranes were characterized using sessile-drop contact angle, tabletop scanning electron microscopy (SEM), and gravimetric methods, respectively. Subsequently, the antifouling performance of these synthesized membranes was assessed by exposing them to a solution containing sucrose as a neutral model foulant and humic acid as an anionic foulant. The incorporation of zwitterion-functionalized graphene oxide nanoparticles improved the surface wettability of the nanocomposite membrane, enhancing its resistance to sucrose fouling. This was supported by a reduction in flux declination ratio (e.g., 40.6 % for pristine PES, 29.7 % for 1.0 % (w/w) Gly/GO PES, and 33.1 % for 1.0 % (w/w) diGly/GO PES) and an increase in flux recovery ratio (67.2 % for pristine PES, 79.7 % for 1.0 % (w/w) Gly/GO PES, and 80.0% for 1.0 % (w/w) diGly/GO PES). The improvement in antifouling characteristics is attributed to the formation of a hydration layer on the membrane surface, which inhibits sucrose deposition. However, zwitterion-functionalized PES nanocomposite membranes displayed a higher affinity for anionic humic acid, resulting in a substantial flux decline and a lower flux recovery ratio. Overall, this research provides insights into the roles of surface wettability and the charge interactions between solutes and the membrane surface, both of which are crucial factors in determining fouling severity and the restorability of spent membranes.