Novel superhydrophilic antifouling PVDF-BiOCl nanocomposite membranes fabricated via a modified blending-phase inversion method

Abstract

PVDF nanocomposite membranes prepared by the widely used conventional blending-phase inversion method generally suffer from nonuniform distribution and low exposure of additive nanomaterials, resulting in unsatisfactory hydrophilicity and antifouling capability. Herein, we developed a modified blending method that incorporates the water-triggered precipitation (resembles phase inversion) of the nanomaterials into PVDF phase inversion. PVDF-bismuth oxychloride (BiOCl) nanocomposite membranes were prepared by dissolving KCl and Bi(NO3)3 in the PVDF dope solution to enable the simultaneous precipitation of PVDF and hydrophilic BiOCl in the coagulation bath. Characterizations demonstrated that the nanocomposite membranes are superhydrophilic, mainly attributed to the surface-preferential precipitation of BiOCl. Crossflow filtration results showed that the nanocomposite membrane had a pure water flux of 854 L m-2 h−1 bar−1 (LMHB) and a humic acid separation flux of 780 LMHB, much higher than 377 and 240 LMHB of the plain membrane. For bovine serum albumin (BSA) separation, the nanocomposite membrane achieved a quasi-steady state flux of 370 LMHB and a rejection ratio of ~90% during three test cycles. In contrast, the hydrophobic plain membrane was severely fouled by BSA, evidenced by a rejection ratio lower than 40%. We proposed a new mechanism that illustrated the effects of protein-membrane interactions and filtration hydrodynamics that well explained the filtration results. The nanocomposite membrane also possessed a 3-fold higher capacity for Cr (VI) adsorption than the plain membrane. These results suggest that this modified blending-phase inversion method could fabricate nanocomposite membranes with great separation and antifouling capability, and multifunctionality.