Decoding enhanced oily wastewater purification and photocatalytic self-cleaning performance of magnetic field-strategized composite membranes with surface-localized CoFe2O4@PDA

In this study, magnetic polydopamine-coated CoFe 2 O 4 composites (CoFe 2 O 4 @PDA) were strategically assembled onto a porous polymer substrate via a magnetic-field-assisted non-solvent induced phase separation (MNIPS) process to construct photoactive self-cleaning membranes for efficient oil–water separation. The synergistic integration of CoFe 2 O 4 and PDA not only enhanced surface hydrophilicity but also promoted photocatalytic activity, enabling visible-light-driven degradation of organic foulants and high membrane self-cleaning efficiency. Systematic characterizations confirmed that the applied magnetic field effectively regulated nanoparticle alignment on the membrane surface, generating a rough, hydrophilic structure with excellent underwater superoleophobicity. The optimized composite membrane achieved a pure water flux of 4266.0   L·m⁻²·h⁻¹·bar⁻¹, 1.95 times higher than that of the pristine substrate, while maintaining separation efficiencies above 99% for various oil-in-water emulsions. Complementary molecular dynamics simulations further demonstrated that CoFe 2 O 4 @PDA nanoparticles reorganize interfacial hydrogen-bond networks, reduce oil–water interfacial tension, and thus promoted permeance and oil rejection of membranes. Under visible-light irradiation, a flux recovery ratio exceeding 99.0% was maintained over five consecutive filtration and self-cleaning cycles, showing outstanding photo-regenerability. Mechanistic studies revealed that CoFe 2 O 4 @PDA significantly enhanced the generation of reactive oxygen species (•OH and •O 2 ⁻), facilitating foulant degradation and surface renewal. This work provides molecular-level understanding and a scalable strategy for designing next-generation photoactive membranes for sustainable oily wastewater treatment.