An emulsion demulsification membrane with heterogeneous wettability structure for efficient oil-water separation

The efficient separation of emulsified oily wastewater was of significant practical importance. However, it was hindered by factors such as low separation flux and severe membrane fouling, making the separation process highly challenging. Inspired by the in-situ nanocomposite strategy mediated by bionic mussel adhesion, this study used oxidants to induce rapid deposition of dopamine (DA) and fulvic acid (FA) on the polyvinylidene fluoride (PVDF). Combined with in-situ growth technology, ZIF-8 nanoparticles were anchored on the coating surface to construct a PVDF-based composite membrane with heterogeneous wettability structure was constructed which were composed of lipophilic ZIF-8 protrusions, hydrophilic layer, and PVDF basement membrane. In the process of separating oil-bearing lotion, the raised ZIF-8 helps to capture and collect oil droplets, and works in synergy with the screening effect of the hydrophilic layer. The demulsification capability was enhanced by the unbalanced force derived from the wettability discrepancy between the protrusions and the substrate, thus enabling efficient separation of emulsions. The optimized composite membrane efficiently separates light/heavy emulsions, with a rejection rate exceeding 99.4 %. The n-hexane-in-water emulsion maintained a high recovery flux ( FRR ) of 92.3 % after 30 cycles. Molecular dynamics simulations confirm that the membrane's hydrophobic/hydrophilic architecture actively promotes emulsion demulsification and oil droplet separation. This study provides precious view into the design of emulsion separation membranes and advances in separation technologies.