Interfacial Synergistic Engineering of Piezoelectric PVDF/GO/Bi2WO6 Nanofiber Membranes: Coupling Mechanisms of Wetting-Induced Segregation and Electric Field-Assisted Demulsification

Abstract

To address the bottleneck of sudden drops in flux and separation efficiency caused by dispersed water droplets during water-in-oil emulsion separation, this study utilized electrospinning technology to fabricate a PVDF/GO/Bi2WO6 composite nanofiber membrane (PGB 48) that combines thermodynamic selective wetting and sieving with kinetic piezoelectric effects. The synergistic interface effects between GO and Bi2WO6 not only optimize the membrane’s porous network but also efficiently induce the oriented growth of the polar all-trans β crystal phase through interfacial confinement and heterogeneous nucleation, enhancing the membrane’s intrinsic piezoelectric activity. Dynamic fluid shear during continuous separation triggers a subtle strain-induced piezoelectric response in the flexible nanofibers. By utilizing the dynamic changes in local micropiezoelectric potential and the redistribution of interfacial charges, the membrane demonstrates effective in situ demulsification and reduced droplet adhesion. Benefiting from interfacial charge redistribution and in situ piezoelectric field-assisted demulsification, the membrane achieves enhanced separation efficiency and antifouling stability. Owing to its intrinsic hydrophobic-oleophilic properties, the PGB 48 membrane delivers a separation flux up to 19,060 L/(m2·h) and a separation efficiency as high as 99.91% for gravity-driven stratified oil–water mixtures. In contrast, when treating surfactant-stabilized water-in-oil emulsions, the permeate flux drops to 3,235 L/(m2·h), but the separation efficiency remains at 98.16%. This study combines thermodynamic multistage barriers with kinetic polarization electric fields to overcome the susceptibility to fouling inherent in conventional membranes, providing a long-term antifouling separation solution for the treatment of industrial oily wastewater.