Bio-inspired fabrication of superhydrophilic and underwater superoleophobic alumina membranes for highly efficient oil/water separation

Inspired by fish scales, superhydrophilic and underwater superoleophobic alumina membranes were fabricated in this study. Dopamine deposited on the surface of alumina membranes through immersion over time, and then crosslinking reaction occurred with polyethyleneimine (PEI), which was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. It induced the modified layer coated on the membrane surface. Values of water contact angle of the modified alumina membranes were similar to 0 degrees in air. Values of underwater oil contact angle reached 155 degrees, which indicated it was superhydrophilic and underwater superoleophobic. More particles engendered with the increase in the reaction time with PEI, which induced the decrease in the pore sizes and permeation flux. All values of oil rejection were higher than 98.5%. No obvious deterioration of permeation flux could be found. The rejection hardly suffered a sharp decline over 800 min. It indicates that the modified layer can firmly stick to the alumina membranes. Therefore, the as-prepared alumina membrane is promising for practical oil/water separation.