Potocatalytic antifouling membrane with dense nano-TiO2 coating for efficient oil-in-water emulsion separation and self-cleaning

Herein, a dense rutile nano-titanium dioxide (TiO2) coating was constructed on the nonwoven fabric (NWF) membrane surfaces via the bio-inspired TiO2 sol-gel method. The mineralization of nano-TiO2 was large-scale and uniform on the non-woven fabrics (NWF) surface, reducing membrane surface roughness and pore sizes; nevertheless, largely improving the dynamic water super-wetting, water penetration, and underwater oil repellency due to the excellent water affinity. Nuclear magnetic resonance (NMR) revealed the hydration layer of the NWF was reinforced by the surface-mineralized nano-TiO2, thus preventing the bovine serum albumin (BSA) and emulsified oil droplets from fouling. Even after the 180 min of continuous emulsion separation, the mineralized NWF (TiO2-PDA/PEI-NWF-M) only suffered from the mild decline of permeation fluxes from ∼55 L/m2•h to ∼43 L/m2•h and oil rejection from ∼94% to ∼83%, respectively. After illuminated under UV light, it was recovered successfully because of the in-situ generation of reactive species (e.g. •OH, •O2− and 1O2) on TiO2 weakened the interaction of foulants on the membrane surface. The photoactive self-cleaning provided the TiO2-PDA/PEI-NWF-M with better efficiency of oil-fouling reduction, permeation fluxes recovery, and oil removal than those of simple water and harsh NaClO washing. Most importantly, the TiO2-PDA/PEI-NWF-M maintained its surface physical and chemical characteristics after vigorous cross-flow shearing for 48 h. It provided the practical potential in developing the high-efficient and free-chemical self-cleaning with the high and stable flux recovery for the tricky crude oil/water emulsion remediation.