In-situ growth of robust and superhydrophilic nano-skin on electrospun Janus nanofibrous membrane for oil/water emulsions separation

It is difficult for composite fibrous membranes to achieve up to 99.5% separation efficiency for oil/water emulsions under cycling separation. Herein, a simple method is developed to in-situ grow surperhydrophilic nanocoating on a single electrospun polyvinylidene fluoride (PVDF) fiber surface for fabricating asymmetric wettable Janus PVDF fibrous membranes. Particularly, polysaccharide fluids with zwitterionic polymer chains are generated from the nanofiber subsurface in an inside-out way during the electrospinning process, forming the robust superhydrophilic nanocoating (<5 degrees) under a synergistic effect of both the electric field force and selfmigration feature of N-carboxymethyl chitosan fluids (CMCfs). Benefiting from opposite wettability of the PVDF Janus membrane, the results show that the as-prepared Janus membranes with asymmetrical wettability exhibit excellent separation efficiency (S/E) (>99.5 %), a high flux (up to 4325 L m(-2) h(-1) bar(-1)), antibacterial activity (>99%) and antifoul properties. Moreover, the obtained Janus membranes own surprising flux cycling stability and retained 99.5% separation efficiency after 12 cycles without any treatment, indicating that the multi-arm polysaccharide fluids acted as the water channel in such membrane and accelerated the flow of water molecules. The Janus PVDF composite membranes have potential applications for oily wastewater treatment and water purification in the future.