Janus poly(vinylidene fluoride)-graft-(TiO2 nanoparticles and PFDS) membranes with loose architecture and asymmetric wettability for efficient switchable separation of surfactant-stabilized oil/water emulsions

Janus membranes, with extremely asymmetric wettability, superior flux and rejection, facile fabrication route, and versatile in complex environment, is urgently needed in fields of ideal oil/water separation. In this work, a facile poly (vinylidene fluoride)-graft-(TiO2 nanoparticles and 1H, 1H, 2H, 2H-perfluorodecyltri-ethoxysilane) (PVDF-g-(TiO2-PFDS)) membrane with loose architecture and asymmetric wettability was successfully fabricated by one-step surface grafting and further single-side chemical vapor deposition (CVD) strategies. Amino-functionalized TiO2 (TiO2–NH2) nanoparticles immobilized could not only improve surface energy and roughness of the PVDF-g-poly(acrylic acid) (PAA) membrane, but also decrease pore size adequately. PFDS was further deposited on one side of PVDF-g-TiO2 NPs membrane for constructing asymmetric interface. The fabricated Janus membrane showed superhydrophilic (a water contact angle of 0°) and superhydrophobic (a stable water contact angle of 151°) properties on forward/reverse surfaces. These characteristics endowed the membrane with high separation flux of ∼2500 L·m-2·h-1 under 0.1 MPa, and high rejection rate of above 99.70% for separating surfactant-stabilized dodecane-in-water and water-in-chloroform emulsions, respectively. Furthermore, the PVDF-g-(TiO2-PFDS) membrane showed excellent cycling performance during separation process. This work shows a potential way to fabricate Janus membranes with dual wettability for efficient oil/water separation facilely. [Display omitted] •TiO2 NPs improved surface energy, roughness, as well as decreased pore size.•A superhydrophobic membrane surface was fabricated via CVD strategy.•Janus PVDF-g-(TiO2-PFDS) membranes was fabricated.•PVDF-g-(TiO2-PFDS) membranes possessed ultra-low oil adhesion force.•It could treat both oil-in-water and water-in-oil emulsions effectively.