Zwitterionic polyvinylidene fluoride membranes with strong underwater superoleophobicity and oil-fouling resistance for oily water purification

Polyvinylidene fluoride (PVDF) membrane offers excellent potential for efficient separation and purification of O/W emulsions. However, oil-fouling presents a major obstacle to its further application. Herein, a strong un-derwater superoleophobic surface was engineered to efficiently inhibit oil-fouling. PVDF-graft-poly(2-(dime-thylamino) ethyl methacrylate) (PVDF-g-PDMAEMA) membranes were first fabricated via vapor-induced phase separation (VIPS), in which the nascent liquid film was left in a vapor bath for a predesigned time (t(e)). The surface roughness increases by an order of magnitude when t(e) increases from 0 to 240 s, and the underwater oil contact angle (UWOCA) correspondingly increases to more than 150?. However, it declines with time gone until the oil droplets on the underwater membranes were swallowed up. After surface zwitterionicalization by the reaction between PDMAEMA and 1, 3-propane sulfonate, a strong underwater superoleophobic surface was obtained, even after being soaked in water for 24 h. It endows the zwitterionic membrane with superior crude oil/water emulsion separation (with a flux of 749.7 +/- 44.8 L m(-2) h(-1) and separation efficiency of 99.4 +/- 0.1%) and excellent oil-fouling resistance (with a flux recovery rate of more than 90%), improving the potential value of porous membranes in oily water treatment.

Automated summary

This study successfully addressed the oil fouling issue of PVDF membranes by engineering a strong underwater superoleophobic surface. PVDF-g-PDMAEMA membranes were fabricated and their underwater superoleophobicity was enhanced through surface zwitterionicalization. The modified membranes exhibited excellent separation performance for oil/water emulsions and showed superior resistance to oil fouling.