Gravity-driven oil/water separation using PVDF-HFP electrospun nanofiber membranes
With increasing industrialization and lenient waste disposal practices, oil-contaminated wastewater has become a significant environmental concern. Oil spills associated with oil exploration and transportation will continue to pose an ecological threat as long as we depend on oil for energy needs. Electrospun nanofiber membranes have a high surface area, porosity, mechanical strength, and tunable nanofiber structure and have been increasingly employed in membrane filtration and desalination systems. A well-designed superhydrophilic and underwater superoleophobic membrane could overcome several challenges associated with the traditional membrane processes for oil/water separation. In the present work, electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber membranes blended with tungsten oxide (WO3) nanoparticles and surface-coated with polydopamine nanostructures (PDA) were fabricated and tested for gravity-driven oil/water separation. PDA hybrid coating resulted in superhydrophilic membranes, which facilitated the preferential penetration of water while rejecting the oil when filtered as an oil-in-water emulsion. When filtered (under gravity) with 1000 mg/L mineral oil, the WO3-blended/PDA-coated PVDF-HFP membrane achieved the highest water flux of ~145 L m-2 h-1 (LMH), followed by the PDA coated pristine PVDF-HFP membrane reporting ~80 LMH. As being hydrophobic, the pristine PVDF-HFP membrane showed no flux during the gravity filtration of 1000 mg/L of mineral oil. Similarly, the WO3-blended/PDA coated PVDF-HFP membrane demonstrated the highest oil removal efficiency of approximately 97%, whereas the PDA coated pristine PVDF-HFP membrane reported ~92% oil rejection. Thus, the fabricated novel nanofiber membrane results in low energy consumption and a low propensity for membrane fouling.