Bi-continuous positively-charged PVDF membranes formed by a dual-bath procedure with bacteria killing/release ability

Abstract

• Original positively-charged copolymers are synthesized. • Positively charged membranes are formed by dual-bath procedure. • Bacteria killing occurs upon contact with the membrane’s surface. • Membranes can be regenerated by washing with saline solution. • Membranes can kill while rejecting bacteria. This work reports the synthesis of a unique positively-charged copolymer obtained from the reaction between iodomethane and a random copolymer of styrene and 4-vinylpyridine. This copolymer, referred to as qP(S- r -4-VP), was fully characterized by 1 H NMR, FT-IR, XPS and GPC, and then mixed with poly(vinylidene fluoride) (PVDF) to form porous membranes able to kill bacteria upon contact. Membranes were prepared by a dual-bath procedure using methanol (10 min) and water (24 h). They exhibited typical bi-continuous structure with large pores (mean pore flow diameter: 0.2–0.45 µm) that decreased with the copolymer content, and large porosity (77%-80%). The presence of the copolymer on the membrane surface was ascertained by FT-IR. All membranes exhibited a high water contact angle in air (>140°), but hydration capacity was enhanced with the copolymer content in the membrane (from 10 mg/cm 3 for the virgin membrane up to 225 mg/cm 3 for modified membranes). The surface charge of the membrane increased with the copolymer content. Q3 membrane (containing 3 wt% copolymer) was selected as the best membrane able to kill various bacteria including Escherichia coli , Stenotrophomonas maltophilia and Staphylococcus epidermidis . Besides, washing with a saline solution of sodium citrate or sodium hexametaphosphate disturbed electrostatic and hydrophobic interactions between dead bacteria and membrane surface, making bacterial release possible. Membrane regeneration properties were also demonstrated from multiple killing/release cycles. Finally, it was shown that membranes were able to kill bacteria during a dead-end filtration process, while achieving 100% rejection. The material and membrane presented in the frame of this work could be of interest to decrease the pathogenicity of a feed during separation