Synergistic effects of matrix-anchoring and surface-segregation behavior of poly(N-vinylpyrrolidone)-grafted-silica filler for PVDF membrane performance improvement

Three dimensional (3D) poly(N-vinylpyrrolidone)-grafted-mesoporous silica (MS-g-PVP) was first synthesized, and explored as a filler for enhancing filtration performance of poly(vinylidene fluoride) (PVDF) composite membrane in this study. Membrane structure, interfacial property and filtration performance of the composite membranes were studied in detail. The relationships of mesoporous silica properties with membrane performance was systemically revealed. The 3D morphology of MS-g-PVP, that stably anchored in PVDF, endowed the membrane with defects-free, uniform and straight finger-like pores structure, and thus greatly enhanced water flux (maximized to 80.7 L m^-2h⁻¹, over 5.7 times than that of pristine PVDF membrane), without BSA rejection efficiency changing (98.6%). Three reasons can be accounted for the membrane performance improvement: i. The hydrophilic MS-g-PVP well dispersed in PVDF membrane matrix, and facilitated the formation of the evenly porous structure for the composite membrane; ii. Surface segregation of MS-g-PVP with the amount and diversity of oxygen-/nitrogen-containing groups on membrane surface, thus improving membrane surface hydrophilicity with contact angle decreasing from 89.0^° to 70.6^°; iii. Numerous mesopores inside of MS-g-PVP provided additional water pathways. In addition, these synergistic effects also enhanced the fouling-resistance of PVDF/MS-g-PVP membrane, whose flux recovery ratio maintained at 85.8% even after three “fouling-cleaning” dynamic BSA solution (0.2 g L^-1) filtration cycles.