Superhydrophilic and Oil-Resistant SiO₂/PU Fiber Membrane for Oil-In-Water Emulsion Separation under Gravity

A polyurethane membrane with interlayer channels was developed through electrospinning to separate oily sewage. To enhance its hydrophilicity, hydrophilic silica particles were grafted onto the fiber surface, creating a rough surface. This was done by treating the membrane with oxygen plasma to generate active sites, which were then coupled with 3-aminopropyltriethoxysilane, followed by adding the membrane to a hydrolytic solution of tetraethyl orthosilicate. The resultant membrane had a low water contact angle of 23.3° and excellent underwater oleophobicity, with a high-underwater oil contact angle (varied from 155.9 to 159.7°) and underwater oil sliding angle (ranged from 4.0 to 4.6°) for different types of oils. In addition, the prepared membrane had a good moisture-evaporation rate (4.2 g/h) and water-absorption capacity (273%). It is also oil-resistant and self-cleaning in water, and could efficiently separating oil-in-water emulsion under gravity, with an initial separation flux of 2864 L/m²/h. During cyclic separation of emulsion, the membrane had the oil-retention rate of more than 99.0%, and the final separation flux of the membrane was maintained at 25 L/m²/h.