Poly(vinylidene fluoride) membranes with underwater superoleophobicity for highly efficient separation of oil-in-water emulsions in resisting fouling

Abstract

Oil droplets can adsorb on the surface or enter the pore channels during membrane separation, causing a decrease in water flux and increasing the number of washing and replacements, thus increasing costs. So, membrane fouling seriously limits the use of the membrane in the purification of wastewater containing oils. Generally, the underwater superoleophobic surface provides better resistance to oils, which can be fabricated by the synergistic effects of the rough structure and hydrophilic groups are required. Here, poly(vinylidene fluoride)/poly(2-hydroxyethyl methacrylate) (PVDF/PHEMA) composite membranes with the continuous sponge-like rough structure were prepared by the vapor-induced phase separation process (VIPS), and then they were furthermore co-deposited by tannic acid (TA) and N-aminoethyl piperazine propane sulfonate (AEPPS). The zwitterionic surfaces with excellent underwater anti-oil adhesion ability can efficiently separate crude oil-in-water having the flux 1056 ± 102 L m−2 h−1 bar−1 and toluene-in-water emulsions having the flux of 1593 ± 163 L m−2 h−1 bar−1, the separation efficiency is more than 99%. Moreover, they exhibit excellent underwater anti-oil adhesion ability, excellent stability, and reversibility. Our work develops rough and porous surfaces with stable underwater superoleophobicity in an efficient way, which enables the resulting membranes to be used in the continuous purification of oily wastewater.