Robust and Recyclable CTZ@PVDF Membrane with Superior Emulsion Separation Efficiency and Anti-Fouling Properties

Wastewater treatment represents a critical challenge in environmental protection, with the effective separation of oil-in-water emulsions being a pivotal step toward sustainable water management. Polyvinylidene fluoride (PVDF) holds great promise for emulsion separation due to its excellent chemical stability. However, the inherent hydrophobicity of PVDF often leads to severe oil fouling and compromised performance. In this study, we addressed this limitation by employing tannic acid (TA) as a hydrophilic modifier to construct a TA-Co 2+ coordinated network integrated with a zeolitic imidazolate framework (ZIF-8) through layer-by-layer self-assembly on a PVDF substrate. The resulting CTZ@PVDF membrane exhibited hydrophilic properties with a water contact angle of approximately 8°, coupled with underwater superhydrophobicity with underwater oil contact angle ≈ 170° and strong resistance to oil adhesion. The CTZ@PVDF membrane demonstrated high efficiency in separating various oils, including kerosene, gasoline, soybean oil, and diverse organic solvents, achieving oil rejection rates exceeding 98% for both surfactant-free and surfactant-stabilized emulsions. Furthermore, after 10 separation cycles, the membrane maintained excellent separation efficiency, and its separation flux recovery rate (FRR) could be restored to over 96% of the initial value through simple cleaning. These results showed a substantial enhancement in hydrophilicity and separation performance compared to the unmodified PVDF membrane. The developed strategy not only provided an effective pathway for designing advanced wettability-controlled materials but also offered broad potential for the treatment of oily wastewater and complex emulsion separations.