Eco-friendly and one-step modification of poly(vinylidene fluoride) membrane with underwater superoleophobicity for effective emulsion separation

In this study, poly(vinylidene fluoride) (PVDF) microfiltration membrane was modified by an eco-friendly and low-cost mussel-inspired method for applications in oil/water separation. Catechol (CA) and polyamines, instead of dopamine (DA), were utilized to modify the membranes based on a facile one-step solution-immersion process. Similar to the oxidation polymerization of DA, polyamines can react with CA via Schiff base/Michael addition reaction. A homogeneous coating with micro-nano structures and superior hydrophilicity can be formed on the surface of the membrane and the inner walls of its holes. The membrane with a water contact angle of nearly 0 degrees and a water flux above 8000 L/m(2) h was obtained after being modified with 5 mM CA and tetraethylene pentaamine (TEPA) for 24 h. The micro-nano scale roughness and the superior hydrophilicity contributed to an excellent underwater superoleophobicity with oil contact angles larger than 150 degrees and low adhesion to various oils. The as-prepared membrane was applied to separate a series of oil-in-water emulsions, and a high separation efficiency larger than 99.4 % as well as extraordinary antifouling property without discernible decay after ten cycle tests were demonstrated. Moreover, the functional coating shows good stability in acid and alkali environment with the pH values between 0 and 11, and has few impacts on the mechanical and thermal properties of the pristine membrane. Therefore, the proposed facile and low-cost preparation of the underwater superoleophobic microfiltration membrane shows great potential in practical oily wastewater treatment.