Biomimetic Layer-By-Layer Assembled PVDF Membrane with Superhydrophilicity and Antifouling Property for Efficient Oil/Water Separation

Environmental pollution resulting from oil–water emulsions presents a serious threat to both human activities and ecosystems. Although the superwetting membranes are widely regarded as a promising solution for separating oil-in-water emulsions, membrane fouling remains a critical challenge that hinders their long-term practical application. In this study, a hydrophilic copolymer, PHEAA-co-PVP, was synthesized via the copolymerization of hydroxyethyl acrylamide (HEAA) and vinylpyrrolidone (VP). Hydrogen-bonding-induced layer-by-layer (LbL) self-assembly of dopamine (DA) and PHEAA-co-PVP was subsequently used as a biomimetic strategy to functionalize polyvinylidene fluoride (PVDF) membranes. The results revealed that the incremental coating degree enhanced the pore-blocking effect, leading to a gradual reduction in the mean aperture size of the membranes. The introduced coating markedly enhances the surface hydrophilicity of the membrane, as evidenced by an initial water contact angle as low as 14.9°, while simultaneously conferring underwater superoleophobicity to the separation membrane. The flux of the modified membranes was found to initially increase and subsequently decrease with increasing coating degree, as shown by permeation experiments. Furthermore, the membranes showed exceptional separation capability for a range of oil-in-water emulsions, achieving over 98% oil rejection. Thanks to the robust hydration capability of the self-assembled coating, the membranes exhibited superior antifouling performance during cyclic filtration of oily emulsions, attaining a high flux recovery ratio of up to 96%. This study demonstrates a strategy for fabricating superwetting membranes through LbL self-assembly, enabling highly efficient oil–water emulsion separation.