Underoil superhydrophilic nanofiber-based composite aerogels for efficient separation of water/oil mixtures and water-in-oil emulsions

Abstract

Oily wastewater has caused serious environmental problems. To achieve efficient separation of oil/water mixtures and surfactant-stabilized water-in-oil emulsions, electrospinning, directional freeze-casting and thermal treatment techniques were combined to fabricate anisotropic and aligned nanofiber-based composite aerogels with underwater superoleophobicity and underoil superhydrophilicity. No toxic crosslinking agents or organic solvents were used during the whole fabrication process. The composite aerogels without any surface modification possessed the ability to selectively absorb water from oil/water mixtures to realize effective separation oil and water. Furthermore, the composite aerogels could separate surfactant-stabilized water-in-oil emulsions by gravity-driven filtration. When used for gravity-driven separation of Span80 stabilized water-in-petroleum ether emulsion, the flux and corresponding separation efficiency reached 2423 L·m−2·h−1 and 99.8 %, respectively. The used composite aerogel could be readily recycled by rinsing and freeze-drying without using any organic solvent, because it displayed underoil superhydrophilicity and excellent anti-oil property. Differing from the separation materials that have been previously documented, the nanofiber-based composite aerogels could act as both absorption materials and gravity-driven filtration materials. In summary, the composite aerogels developed in this study show great potential for efficient separation of oil and water.