PVDF-Modified TiO₂ Nanowires Membrane with Underliquid Dual Superlyophobic Property for Switchable Separation of Oil–Water Emulsions

Separation membranes with underliquid dual superlyophobicity have recently caused widespread concern due to their switchable separation of oil–water mixtures and emulsions. However, the fabrication of the reported underliquid dual superlyophobic membranes is difficult, and the design of the underliquid dual superlyophobic surface of these membranes is challenging because of their complex surface composition. Theoretically, underliquid dual superlyophobicity is an underliquid Cassie state attainable by the synergy of the underliquid dual lyophobic surface and the construction of a high-roughness surface. Herein, we fabricated an underliquid dual superlyophobic membrane by combining underliquid dual lyophobic polyvinylidene fluoride (PVDF) and TiO2 nanowires. PVDF-modified TiO2 nanowire membranes with underliquid dual superlyophobicity were prepared via a simple adsorption and filtration approach. PVDF was coated onto TiO2 nanowires to form a PVDF layer with a thickness of 6 nm. The PVDF modification provided flexibility to the fragile TiO2 nanowires membrane and changed its wettability from underwater superoleophobicity/underoil superhydrophilicity to underliquid dual superlyophobicity. The PVDF-modified TiO2 nanowires membrane efficiently separated both oil-in-water and water-in-oil emulsions. The binary cooperative effect between the TiO2 nanowires and the coated PVDF layer was responsible for the underliquid dual superlyophobicity.