Protein-induced silica coated PVDF membrane with long-term acid resistance and outstanding anti-oil-fouling performance for highly efficient separation of strongly acidic emulsion

Rare earth mining produces a large amount of acidic oily wastewater, which causes serious environmental pollution. Developing an acid-resistant oil–water separation membrane is an effective way to solve the above problems. In this work, we successfully construct a protein-induced silica coating on polyvinylidene fluoride (PVDF) membrane with the aid of adhesion protein for highly efficient separation of acid emulsion. The obtained coating is composed of ovalbumin (OVA), tannic acid (TA), TiO 2 , and SiO 2, which can endow the PVDF membrane with excellent underwater superoleophobicity and desirable acid resistance. Moreover, the modified membrane has excellent anti-oil-adhesion property, which can keep withstand fouling even an oil droplet is continuously squeezed into the membrane for 2 h under acidic conditions. The outstanding anti-oil-adhesion property is due to the bound water of the multilayer coating, which is confirmed by low field-nuclear magnetic resonance (LF-NMR). The flux recovery can reach up to 98 % and oil rejection rate can reach up to 99.7 % toward strongly acidic emulsion. In addition, the multilayer coating also possesses good stability, which can withstand ultrasonic treatment and washing. Considering the mild preparation process without expensive/complex equipment and the desirable performance, this strategy may become a powerful tool for preparing acid-resistant membranes for efficient treatment of acidic emulsion.