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

Abstract

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 µm, 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.

Fabrication of ultrafast temperature‐responsive nanofibrous hydrogel with superelasticity and its 'on–off' switchable drug releasing capacity

“…In one of our recent researches, 28 a hydrophilic nanofibrous aerogel with hierarchical porous structure was fabricated by the fibrous freeze‐shaping technique, 26 that is, freezing the dispersion of shortened electrospun poly(vinyl alcohol) (PVA)/tetraethyl orthosilicate (TEOS) composite nanofibers in t ‐butanol, followed by freeze‐drying to remove the formed solvent crystals and heat‐treatment. As silica‐based crosslinking points inside the nanofibers and chemical linkages between them were formed through alkali‐catalyzed in situ sol–gel reaction of TEOS during the heat treatment, the hydrophilic nanofibrous aerogel became a nanofibrous hydrogel with the ESR of more than 50 when it was immersed into water.…”

From 1D Nanofibers to 3D Nanofibrous Aerogels: A Marvellous Evolution of Electrospun SiO2 Nanofibers for Emerging Applications

“…11 h, after repeated separation experiment for 10 cycles, the aerogel can still efficiently separate oil–water emulsion, highlighting that aerogel also had excellent anti-pollution performance. In addition, other organic/SiO 2 hybrid nanofibrous aerogels have been developed using similar methods and their applications in the field of oil–water separation have been explored [ 204 , 205 ].…”

Preparation of porous PTFE/C composite foam and its application in gravity‐driven oil–water separation

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] In particular, gravity-assisted oil-water separation has a high application value. [14][15][16][17][18][19][20] The key to gravity-assisted oil-water separation is the selection of filtration media exhibiting extreme wettability. Porous superhydrophobic materials as ideal filtration media with advantages of low energy input and superior separation performance offer a more exciting application prospect, compared with traditional treatment methods, such as oil skimming, centrifuging, coalescing, floating and so on.…”

“…Due to increasingly serious water pollution caused by discharge of industrial wastewater with oil or oil spill accidents, more and more attention has been focused on oil–water separation 1–13 . In particular, gravity‐assisted oil–water separation has a high application value 14–20 . The key to gravity‐assisted oil–water separation is the selection of filtration media exhibiting extreme wettability.…”