Freely switchable super-hydrophobicity and super-hydrophilicity of sponge-like poly(vinylidene fluoride) porous fibers for highly efficient oil/water separation.

Highly efficient oil/water separation ability is a prerequisite for the actual application of the membranes in oily sewage treatment, which is closely related to the surface feature and the porous structure of the membranes. In this work, the electrospun poly(vinylidene fluoride) (PVDF) porous fibers were firstly fabricated through blend-electrospinning with poly(vinyl pyrrolidone) (PVP) and then treating in distilled water. The results showed that the fibers exhibited the sponge-like porous structure, and a few PVP was reserved in the fibers due to the relatively good interaction between PVDF and PVP. The fibrous membrane exhibited high porosity, super-wettability with freely switchable super-lipophilicity and super-hydrophilicity. The oil adsorption capacities as well as the oil and water fluxes were measured, and the oil adsorption capacities were varied in the range of 22.7-76.0 g/g, and oil and water fluxes were 54,737.3 and 56,869.9 L/(mh), respectively. Specifically, the PVDF porous fibrous membranes showed excellent separation abilities and they could highly efficiently separate oil from oil-in-water emulsions or separate water from water-in-oil emulsions, accompanied with the extremely high water or oil flux. This work confirms that the PVDF membranes composed of the porous fibers can be used in wastewater treatment.