Highly Hydrophilic Polyvinylidene Fluoride (PVDF) Ultrafiltration Membranes via Postfabrication Grafting of Surface-Tailored Silica Nanoparticles Shuai Liang, † Yan Kang, ‡ Alberto Tiraferri, § Emmanuel P. Giannelis, ‡ Xia Huang,* ,† and Menachem Elimelech* ,§ † State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China ‡ Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, United States § Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06520-8286, United States * S Supporting Information ABSTRACT: Polyvinylidene fluoride (PVDF) has drawn much attention as a predominant ultrafiltration (UF) membrane material due to its outstanding mechanical and physicochemical properties. However, current applications suffer from the low fouling resistance of the PVDF membrane due to the intrinsic hydrophobic property of the membrane. The present study demonstrates a novel approach for the fabrication of a highly hydrophilic PVDF UF membrane via postfabrication tethering of superhydrophilic silica nano- particles (NPs) to the membrane surface. The pristine PVDF membrane was grafted with poly(methacrylic acid) (PMAA) by plasma induced graft copolymerization, providing sufficient carboxyl groups as anchor sites for the binding of silica NPs, which were surface-tailored with amine-terminated cationic ligands. The NP binding was achieved through a remarkably simple and effective dip-coating technique in the presence or absence of the N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) cross-linking process. The properties of the membrane prepared from the modification without EDC/NHS cross-linking were comparable to those for the membrane prepared with the EDC/NHS cross-linking. Both modifications almost doubled the surface energy of the functionalized membranes, which significantly improved the wettability of the membrane and converted the membrane surface from hydrophobic to highly hydrophilic. The irreversibly bound layer of superhydrophilic silica NPs endowed the membranes with strong antifouling performance as demonstrated by three sequential fouling filtration runs using bovine serum albumin (BSA) as a model organic foulant. The results suggest promising applications of the postfabrication surface modification technique in various membrane separation areas. KEYWORDS: ultrafiltration, PVDF, fouling, antifouling, superhydrophilic, nanoparticles, membrane functionalization ■ INTRODUCTION Ultrafiltration (UF) is a membrane separation process extensively used in various fields, such as the food and dairy industry, 1,2 biological purification, 3,4 and water purification, 5-8 where high separation efficiency is required. While membrane filtration processes, such as UF, are widely used, their long-term operation is hampered by the low resistance of the membranes to fouling. Membrane fouling, caused by the adsorption and accumulation of various foulants on a membrane surface or in a membrane matrix during filtration, results in reduced productivity, additional operating costs, and the need for frequent chemical cleaning that shortens membrane life- span. 9-13 Membrane surface hydrophilicity is widely accepted as a dominant factor that governs fouling development on the membrane. 11,12,14 A hydrophilic membrane surface generally has higher fouling resistance compared with hydrophobic membranes. 9-11,13 Polyvinylidene fluoride (PVDF) is extensively used as a UF membrane material in a wide range of applications due to its outstanding mechanical strength, chemical resistance, and thermal stability. 15-17 Nevertheless, the intrinsic hydrophobic property of PVDF is a major challenge for the widespread application of PVDF membranes in separation processes that involve feed solution containing organic and biological substances. The low surface energy of the resultant PVDF Received: April 21, 2013 Accepted: June 24, 2013 Published: June 24, 2013 Research Article www.acsami.org © 2013 American Chemical Society 6694 dx.doi.org/10.1021/am401462e | ACS Appl. Mater. Interfaces 2013, 5, 6694-6703