A dual-biomimetic strategy to construct zwitterionic anti-fouling membrane with superior emulsion separation performance

Developing efficient polymeric membranes for the purification of emulsified oily wastewater is of great significance but still challenging, restricted by low flux and severe membrane fouling. Endowing the intrinsically hydrophobic membranes with excellent hydrophilicity thus robust oil-fouling resistance in a facile and universal manner is highly desired. Herein, inspired by saltwater fish and mussel, we report a delicate zwitterionic surface design via co-assembly of 3-aminopropyldimethylamine oxide (APDMAO) and dopamine. Taking advantage of the direct connected positively charged and negatively charged moieties (N+-O-), APDMAO could strongly interact with water molecules via hydrogen bonds thus form a robust hydration barrier as revealed by molecular dynamics (MD) simulations and sum frequency generation (SFG) vibrational spectroscopy. Besides, APDMAO could bond with dopamine via both covalent and noncovalent interactions to regulate coating behavior and improve coating stability. Owing to the superhydrophilicity of APDMAO and the distinct adhesion of polydopamine, the modified membrane exhibits robust superhydrophilicity, underwater superoleophobicity and anti-oil-fouling capability. Consequently, the resultant membrane achieves an ultra-high water permeability of 5163 L m(-2) h(-1) bar(-1) accompanied with an excellent oil rejection of 99.7% for the separation of mineral oil-in-water emulsion. Additionally, the separation performance remains rather stable during 20 cycles of emulsion filtration. The modified membrane also exhibits desired durability and antibacterial property, demonstrating its great promise in practical oily sewage remediation.