Superhydrophobic ZIF-8@PVDF nanofiber membranes with hierarchical structure for the efficient separation of water-in-oil emulsion

Nanofiber membranes are widely employed for oil/water separation applications. However, these membranes suffer from low rejection rate due to their large pore size failing to capture fine water droplets, compounded by serious membrane fouling from surfactant adsorption in separating emulsified oil. To address these limitations, we presented a hierarchical zeolitic imidazolate frame-work-8@polyvinylidene fluoride nanofiber membranes (ZIF-8@PVDF NFMs) via sequential electrospinning and solvothermal synthesis. The hierarchical structure comprises a separation layer of ZIF-8@PVDF nanofibers and a support layer of PVDF nanofibers. The introduced ZIF-8 nanoparticles on the separation layer not only create micro/nano rough surface, thereby endowing the membrane with superhydrophobicity and underoil superhydrophobicity, but also reduce pore size to improve separation accuracy. Meanwhile, the underlying large-pore PVDF layer ensures rapid oil permeation. Consequently, this hierarchical design achieves outstanding removal efficiency (99.1 %) and high flux (3296.2 L m⁻² h⁻¹) for water-in-n-hexane emulsion under the driving pressure of 20 kPa. Notably, the membrane exhibited robust recyclability with separation efficiency‌ remaining 98.8 % after 10 cycles. The hierarchical nanofiber membrane is a promising candidate for efficient separation of water-in-oil emulsions.