Robust dual-layered omniphobic electrospun membrane with anti-wetting and anti-scaling functionalised for membrane distillation application

Abstract A robust dual-layer superhydrophobic and omniphobic electrospun nanofiber membrane was developed for membrane distillation application, especially with feed that contains surfactant and dissolved organic compounds. 1H, 1H, 2H, 2H-Perfluorooctyltriethoxysilane (FAS) functionalising of the electrospun polyvinylidene fluoride-co-hexafluoropropylene (E-PVDF-HFP) membrane, followed by surface grafting with FAS-functionalised zinc oxide (ZnO) nanoparticles, achieved low membrane water sliding angle with re-entrant morphologies on the membrane surface. Field-emission scanning electron microscopy with energy-dispersive X-ray images revealed the regular and uniform formation of re-entrant structures due to the ZnO nanoparticles. The optimised 25% w/w ZnO (ePFP-25Z) membrane achieved the highest contact angles for water (>161°), oil (131.5° ± 1.8°), ethanol (131° ± 2.9°), had the lowest surface energy (0.75 ± 0.43 mN m−1) and high surface roughness (3.26 μm). The ePFP-25Z membrane maintained a stable membrane distillate flux and salt rejection (>99.9%) even after 80 h operation with 0.1 mM sodium dodecyl sulphate in super-saline solution (1 M NaCl). Anti-scaling and anti-wetting properties were illustrated in the presence of the dissolved organic compounds humic acid and alginate in super-saline feed.