Rational design of Janus nanofibrous membranes with novel under-oil superhydrophilic/superhydrophobic asymmetric wettability for water-in-diesel emulsion separation

Endowing nanofibrous membranes with special wettability has always been the dominant strategy to improve the separation performance for water-in-oil emulsions. In this work, a rational design of deacetylated cellulose acetate/polyvinylidene fluoride (dCA/PVDF) Janus nanofibrous membrane, with asymmetric wettability in either air, water or diesel environment, was developed via sequential electrospinning PVDF and CA membranes followed by alkali treatment. In the process of water-in-diesel emulsion separation, the under-diesel superhydrophilic dCA layer is able to capture the emulsified water and strengthens the demulsification ability of the Janus membrane, while the under-diesel superhydrophobic PVDF layer acts as a water barrier and further improves the separation ability. The Janus membrane therefore exhibited prominent separation performance not only for the water/diesel mixture (separation efficiency 99.98%) but also for the surfactant-stabilized water-in-diesel emulsion with l vol% water (separation efficiency 97.74%). Moreover, the Janus membrane maintained high separation efficiency over 96% after repeated use for 50 times or soaking in corrosive solutions for 24 h. The Janus dCA/PVDF nanofibrous membrane possesses competitive efficiency, reusability and acid/alkali resistance, making it a promising candidate as the separation membrane for the surfactant-stabilized water-in-diesel emulsion.