Amphiphilicity-Tuned Sponge Architecture and Interfacial Adaptability in Electrospun PVDF/PVP/ZIF-8 Nanofibrous Membranes for Durable Dual-Mode Emulsion Separation

Abstract

The efficient separation of stable oil-in-water (O/W) and water-in-oil (W/O) emulsions under challenging conditions remains a critical bottleneck in environmental remediation and industrial processes, often hampered by membrane fouling and limited selectivity. This study utilized electrospinning to incorporate polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP) as robust porous nanofiber scaffolds, enabling the in situ growth of ZIF-8 metal–organic framework (MOF) nanoparticles, thereby fabricating a sponge-like polyvinylidene fluoride/polyvinylpyrrolidone/ZIF-8 nanofiber membrane. This membrane exhibits environmental responsiveness: highly hydrophilic in the oil phase and highly oleophobic in the water phase. When exposed to an oil phase environment, the low surface energy of PVDF and the oleophilic PVP/ZIF-8 components drive the adsorption and penetration of oil molecules on the membrane surface, while in the water phase environment, the water interaction of the PVP chain segments enables the membrane to exhibit underwater superoleophobicity. Comprehensive characterization confirmed the morphology, chemical composition, and pore size distribution of the membrane. Performance evaluation demonstrated that for various oil-in-water emulsions, an extremely high oil permeance of 2566 L m–2 h–1 bar–1 could be achieved, and a separation efficiency of over 99.2%. Additionally, the permeance of water-in-oil emulsions could reach 602 L m–2 h–1 bar–1, with a separation efficiency higher than 98.2%. Furthermore, the composite membrane demonstrated excellent cyclical stability, mechanical robustness, and chemical durability. By revealing a profound correlation between the precisely controlled microscopic structure and emergent macroscopic separation performance, this work advances the design principles for high-performance amphiphilic membranes, offering a promising and sustainable solution for complex emulsion separation challenges.