Mussel-inspired co-deposited L-DOPA/PEI/CNTs/PVDF membrane with hierarchically gradient pores for efficient oil/water emulsion separation

The discharge of oily wastewater and industrial wastewater poses serious threats to aquatic ecosystems and human health, highlighting the urgent need for advanced antifouling membranes capable of efficient oil-in-water emulsion separation. Unlike conventional surface coating or single-component modification strategies, herein, we report a facile strategy to transform hydrophobic PVDF membranes into superhydrophilic ones with hierarchically gradient pores. This approach distinctively exploits mussel-inspired L-3,4-dihydroxyphenylalanine (L-DOPA), rather than dopamine, in combination with polyethyleneimine (PEI) co-deposition and carbon nanotubes (CNTs) nanostructuring, forming a highly stable, multifunctional hydrophilic network that anchors CNTs while synergistically regulating pore size, pore distribution, and surface wettability. As a result, the average pore size decreased from 0.4075 μm to 0.2883 μm, enhancing selective permeability. The optimized L-DOPA/PEI/CNTs/PVDF membrane exhibited an ultrahigh pure water flux of 5367.9 L m −2  h −1  bar −1 and achieved over 99 % rejection of diverse surfactant-stabilized emulsions. Moreover, the membrane demonstrated excellent antifouling, consistently maintaining ≥98 % oil rejection over seven cycles, attributed to the formation of a compact hydration layer. By integrating bio-inspired adhesion chemistry with nanostructured pore-gradient engineering，this study provides a scalable and environmentally relevant route for fabricating high-performance separation membranes, offering strong potential for sustainable oily wastewater treatment and resource recovery applications.