A dual-biomimetic N-oxide-based zwitterionic coating for constructing antifouling membrane with exceptional emulsion separation performance

Abstract

Oil fouling and low flux present significant challenges for membrane application in oil-water separation. Enhancing the hydrophilicity of intrinsically hydrophobic membranes is crucial for improving their antifouling performance through a simple modification. In this study, inspired by the natural mechanisms of saltwater fish and mussels, an antifouling zwitterionic surface was fabricated via co-assembly of a novel N-oxide zwitterionic copolymer (PTODA) and dopamine (DA). The zwitterionic groups in PTODA with the direct link between opposite charges (N⁺-O⁻) create a strong hydration barrier by interacting with water molecules, effectively resisting oil adhesion and enhancing oil-water emulsion permeability. Moreover, the self-polymerization and interaction of catechol groups within DA and PTODA during the co-deposition progress could facilitate the stable anchoring of the zwitterionic copolymer onto the membrane. As expected, the modified membrane thus exhibits excellent hydrophilicity, underwater superoleophobicity, and oil-fouling resistance. Upon optimizing the zwitterionic copolymer composition, the as-fabricated PVDF-PTODA121 exhibited high efficiency of oil-water separation performance, achieving a water permeability of 10,357 L m⁻² h⁻¹ bar⁻¹, a mineral oil-water emulsion flux of 5634 L m⁻² h⁻¹ bar⁻¹, a recovery rate of 90.8 % and a rejection of 99.6 %. Meanwhile, the PVDF-PTODA121 membrane maintained high fouling-resistance and excellent stability under challenging environmental conditions and multiple cycles. Hence, this study presents a novel strategy for fabricating superwetting antifouling membranes through dual-biomimetic methods for achieving efficient separation of oil-water emulsion.