Biomimetic fabrication of PET composite membranes with enhanced stability and demulsibility for emulsion separation

Membrane separation of highly emulsified oily wastewater is a critical requirement, but still challenging due to the poor demulsibility, unstable wettability, and low recyclability of oil/water separation membranes. Herein, inspired by beetles capturing water from the air, an inverse desert beetle-like membrane with excellent demulsibility and significant stability was fabricated using waste poly(ethylene terephthalate) (PET) bottles as building blocks for enhanced emulsion separation. Due to the unbalanced force formed by the surface energy gradient, the small tiny oil droplets of the oil-in-water emulsion can be captured by the superhydrophobic bumps (hierarchical Al2O3 clusters), thus strengthening the demulsification ability of the membrane. Interestingly, the membrane exhibits excellent emulsion separation efficiency (99.91%) and flux (2193.5 L m−2h−1) for surfactant-stabilized oil-in-water emulsions, as well as sustained and stable separation performance, which outperforms conventional single superhydrophilic PDA/PET membrane without superhydrophobic bumps structure. Moreover, a two-stages"growing-jumping" model for the water droplet discharge mechanism was revealed to depict the enhanced stable separation of APP3 membrane, avoiding sticky Wenzel states to destroy the superhydrophobicity of bumps. Thus, the as-designed membrane achieved stable emulsion separation performance in continuous operation, as well as good recyclability. This biomimetic membrane not only shows emergent application potential for emulsion separation, but also provides insights into designing advanced membrane-based separation technology.