Janus stainless steel mesh-based membrane with asymmetric wettability for highly efficient gravity-driven oil-water emulsion separation

With the asymmetric wettability of the membrane due to its unique transmission features and functions, the application of oil-water separation achieved rapid development. Nevertheless, their practical application is severely restricted due to poor mechanical durability and low flux in the absence of external pressure. Herein, the Janus ZIF-8/stainless steel mesh/polydopamine (DZIF-8/SSM/PDA) membrane was successfully prepared using electrodeposition, in-situ growth, and shell ligand exchange reaction methods. The Janus membrane surface was created through the combination of 5, 6-dimethylbenzimidazole (DMBIM) modified superhydrophobic nanoparticles ZIF-8 (DZIF), and PDA, exhibiting underwater superoleophobicity (UWOCA 156◦), superhydrophobicity (WCA 154◦), and excellent anti-oil (light and heavy oil) pollutants ability. By manipulating the molecular repulsion forces on the Janus membrane surface, a stable interfacial hydration layer is created in conjunction with the micro-nano structure. This combination enables the achievement of interfacial demulsification and gravity-driven separation of emulsified oil, according to the Molecular Dynamics (MD) simulation process. The water-in-oil emulsion achieved an oil flux of 601 L·m−2·h−1 with a separation efficiency of 99.1%, while the oil-in-water emulsion demonstrated a water flux of 62 L·m−2·h−1 with a separation efficiency of 99.7%. The Janus DZIF-8/SSM/PDA demonstrated acid and alkali resistance, mechanical stability and reusability, and resistance to E. coli bacteria. Overall, this research anticipates advancing the production of durable asymmetric Janus membranes with superior separation efficiency under gravity, providing a novel solution for oil-water separation.