Construction of gradient SA-TiO2 hydrogel coated PVDF-g-IL fibre membranes with high hydrophilicity and self-cleaning for the efficient separation of oil-water emulsion and dye wastewater

The industrial wastewater filtered by water treatment membranes is very complex in practical applications, therefore, it is a challenge to prepare a membrane with large pore size and high flux that can efficiently separate various wastewater containing pollutants of different scales. To solve this problem, an SA-TiO2 hydrogel-coated PVDF-g-IL composite fibre membrane with super hydrophilicity, anti-pollution, and pH-responsive self-cleaning properties has been designed and prepared by electrostatic spinning and layer-by-layer coating techniques in the present work. The super hydrophilic gel layer on the surface gives the composite membrane efficient separation capability while maintaining rapid passage of the aqueous phase; the underlying PVDF-g-IL fibre membrane is positively charged and removes not only anionic/cationic pollutants by electrostatic repulsion or attraction but also creates an ionic bond with oppositely assigned SA so that the gel layer tightly bond to the base membrane. The PVDF-g-IL@SA-TiO2 membrane achieves stable and efficient separation of oil-water emulsions and dye wastewaters with a high filtration flux while retaining a retention rate higher than ∼95%. After multiple self-cleaning cycles, the ultra-thin gel layer still offers satisfactory durability with ≈100% flux recovery. This study provides a promising new strategy for designing efficient multiple contaminant separation and simpler self-cleaning membranes.