Ternary liquid separation using PVDF nanofiber membranes with tunable structure and surface tension

Wastewater from industrial sources varies greatly in composition. Separating and recycling these waste remains challenging. The efficacy of nanofiber membranes in separating binary liquids has been demonstrated, which in this work we extend to the separation of ternary liquids. Polyvinylidene fluoride (PVDF) nanofiber membranes with different surface tensions were fabricated by electrospinning and surface coating. Membranes made from polyvinyl alcohol and polyacrylic acid (PVA-PAA), and PVDF nanofiber membranes were used in combination for separating water and oils. And pure PVDF and PVDF membranes coated with tetraethyl orthosilicate and decyltrimethoxysilane (TEOS/DTMS) were used together to separate different oils. The structural parameters of PVDF nanofiber membranes, e.g., pore size, thickness, and porosity were easily adjusted to achieve high flux and separation efficiency. For example, the average separation efficiencies for water, oleic acid, and silicon oil were 99.21%, 94.45%, and 84.61%, respectively. Finally, using a two-step setup, a ternary liquid mixture of water, oleic acid, and silicon oil was efficiently separated, which shows great promise for addressing the problem of separating wastewater with mixed compositions.Graphical abstractSchematic illustration of wettability relationship of PVDF membrane