Novel conductive Janus membranes with water diode effect assisted by an electrostatic field for efficient mass transfer and oil-water separation

Membrane separation technology is effective for treating oily wastewater but is limited by the lack of membranes that are both highly permeable and fouling-resistant. Janus membranes, with asymmetric wettability and electrostatic repulsion of charged oil droplets, offer a potential strategy for oil-water separation. This study developed novel electrically enhanced conductive Janus membranes using metal-modified organic membranes to achieve high-efficiency treatment. Conductive metal Janus membranes were fabricated using a straightforward two-step method involving simple electroless nickel plating and surface peeling. The resulting nickel-coated surface of the membrane demonstrated extreme hydrophilicity, underwater oleophobicity, and excellent conductivity (approximately 4.7 Ω). Fascinatingly, the developed membranes exhibited a “water diode” effect, facilitating unidirectional liquid transport without external pressure. Gravity-driven oil-water separation achieved a flux rate of 4874 L m−2 h−1 and over 99 % oil removal efficiency, surpassing most existing studies. During electro-filtration of oil-water emulsions, the conductive Janus membrane as a cathode generated electrostatic repulsion, preventing emulsified oil droplet adhesion. Applying an external voltage increased the flux by approximately 13 times and oil removal efficiency to 99.6 %. The membrane's separation capability remained consistent across six cycle tests, demonstrating robust stability. As all, this work first synthesized conductive “water diode” Janus membranes with high oil-water separation efficiency, offering fresh perspectives on the design and fabrication of Janus membranes as well as on the processes for treating oily wastewater.