Constructing heterogeneously wettable nanofiber membrane for highly efficient oil refining

Superhydrophobic membranes are highly energy-efficient for refining the oil from water-in-oil emulsions. Nevertheless, the poor solvent resistance and the ineffectiveness in separating nano-sized water droplets (below 100 nm) of the superhydrophobic membrane undermine their application in the water/oil separation process, especially for the separation of water-in-dichloromethane (CH₂Cl₂) and water-in-chloroform (CHCl₃) emulsions. Herein, inspired by the desert beetle, we provided a facile approach to enhance the separation efficiency of cross-linked asymmetric nanofiber membrane (CNMs) towards water-in-oil emulsions by well-dispersed superabsorbent sodium polyacrylates (SAPs) particles between nanofibers through coaxial electrospinning technology. Interestingly, the hydrophilic SAPs surrounding by hydrophobic nanofibers form a heterogeneously wettable structure which is like to the structure of desert beetle backs. The unique structure could adjust the surface tension components of the membrane, leading to faster permeance of oil droplets. Moreover, as a superabsorbent resin, SAPs could absorb the nano-sized water droplets in the water-in-oil emulsion, thereby increasing the separation efficiency of the membrane. For water in CH₂Cl₂ emulsions, the finely tailored nanofiber membrane completely removed water droplets larger than 63 nm, demonstrated permeance above 3.5 ×10⁴ L∙m⁻²∙h⁻¹∙bar⁻¹ with significant separation efficiency above 98.8%, and showed fantastic stability in organic solvent, exhibiting strong promise in oil refining.