Under‐Oil Superhydrophilic Poly(vinyl alcohol)/Silica Hybrid Nanofibrous Aerogel for Gravity‐Driven Separation of Surfactant‐Stabilized Water‐in‐Oil Emulsions

For efficient and green separation of surfactant-stabilized water-in-oil (W/O) emulsions, under-oil superhydrophilic poly(vinyl alcohol) (PVA)/silica hybrid nanofibrous aerogel is fabricated by freeze-drying the dispersion of shortened PVA/tetraethyl orthosilicate composite electrospun nanofibers in t-butanol, followed by heat-treatment. Its hierarchical porous structure, observed by scanning electron microscope, consists of major and minor pores with an average diameter of 15.9 and 1.0 mu m, respectively. The silica-based crosslinking structure inside the nanofibers and the chemical linkage between them, evidenced by infrared spectroscopy, endows the nanofibrous aerogel with desirable stability in water and compression recoverability. When it is used for gravity-driven separation of Span80 stabilized water-in-n-hexane emulsion, the flux is 2083 L m(-2) h(-1) and the purity of the separated n-hexane reaches 99.997%, corresponding to the separation efficiency of 99.79%. The nanofibrous aerogel after use is readily recycled by rinsing and freeze-drying, without using any organic solvent, as it possesses under-oil superhydrophilicity and prominent oil antifouling property. Differing from the previously reported separation materials, PVA/silica hybrid nanofibrous aerogel simultaneously acts as gravity-driven filtration material and adsorption material to both absorb their coalesced water droplets and allow the separated oil to penetrate in the separation process.