Under-Oil Superhydrophilic/Superhydrophobic Janus Nanofibrous Membrane for Highly Efficient Separation of Surfactant-Stabilized Water-in-Oil Emulsions

Highly efficient separation of surfactant-stabilized water-in-oil emulsions with both a high separation efficiency and high permeation flux is still challenging. In this work, an under-oil superhydrophilic/superhydrophobic Janus membrane was fabricated by combining an electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane and its modified membrane composited with poly(ethylene glycol) diacrylate (PEGDA). The incorporation of PEGDA is realized by in situ ultraviolet (UV)-initiated polymerization during the electrospinning process, and it endows the upper layer with unique under-oil superhydrophilicity that is very important for the demulsification of water-in-oil emulsions. The under-oil superhydrophobic lower layer serves to block the water and also can promote the permeation flux, because of its oil-absorbing ability. For surfactant-stabilized water-in-n-hexane emulsion (water content of 1 wt %), such a Janus membrane exhibits outstanding separation performance with a separation efficiency of >99.95% and permeation flux of >25 000 L m^-2 h^-1. Moreover, the Janus membrane shows excellent reusability and high applicability for water-in-diesel, water-in-hexadecane, and water-in-petroleum ether emulsions with separation efficiencies of 99.63%, 99.80% and 99.82%, respectively. These features make the Janus membrane a promising candidate as a separation membrane for surfactant-stabilized water-in-oil emulsions.