Dopamine co-coating with fulvic acid on PVDF membrane surface for hydrophilicity improvement and highly-efficient oily water purification

Microfiltration membrane separation technology has been widely employed in the field of oil-water separation because of its low energy consumption. However, the practical applications of polyvinylidene fluoride (PVDF) microfiltration membrane are limited due to its strong hydrophobicity and poor anti-fouling. A superhydrophilic/underwater superoleophobic PVDF microfiltration membrane is prepared through surface co-coating inspired by mussel chemistry. The dopamine (DA) and fulvic acid (FA) generate a hydrophilic coating with hydrophilic functional groups through a mild Michael addition/Schiff base reaction. When the DA/FA ratio is 2/8 and a modification time is 6 h, the pure water flux reaches 8011 L m −2  h −1  bar −1 , the flux of oil-in-water emulsion is 1915 L m −2  h −1  bar −1 , and the rejection is 99.1 %. The retention rate of the membrane for oil-water emulsions containing different oil phases (heavy and light oils) is consistently above 98.5 % and shows high recoveries ( FRR  > 86.6 %) after twenty separations. Modified membranes have high anti-pollution ability for characteristic pollutants in water bodies (for example: BSA, SDS). This work demonstrates a simple surface coating preparation method that has excellent separation performance, and environmental friendliness, offering a promising strategy for large-scale modified membranes to treat oily wastewater.