A highly hydrophilic/underwater superoleophobic layered double hydroxides composite membrane for oil-water emulsion separation: Performance, mechanism, and molecular dynamic simulation

Aimed at the problem of oil substances usually existed as stable emulsified state in oily wastewater, a novel highly hydrophilic/underwater superoleophobic layered double hydroxide (LDH) composite ultrafiltration (UF) membrane was prepared via interfacial polymerization of dopamine and in-situ growth of MgFe-LDH for efficient oil-water separation. Owing to its surface roughness Ra = 45.7 nm) and highly hydrophilicity/underwater superoleophobicity (water contact angle < 10°, underwater oil contact angle > 150°), the LDH composite UF membrane featured with higher flux recovery ratio (expanded by 104.9 %) and better anti-fouling capacity (total fouling ratio decreased from 69.4 % to 37.2 %) than conventional UF membrane. The efficiencies for various types of oil-water emulsions separation exceeding 94 % even after eight cycles and were kept at high fluxes in the range of 310–596 L m −2 h −1 , and the fluxes still remained at 60–86 % after a continuous filtration within 1000 min. For oil-water separation mechanism, on the one hand, the water molecules were aggregated and bonding with hydroxyl groups rapidly via hydrogen bonds to form a hydration layer on LDH composite UF membrane surface, which was conducive to water molecules fast diffusion and penetration. On the other hand, the hydration layer could effectively inhibit oil droplets from contacting membrane surface, thereby enhancing anti-fouling property and ensuring water flux. This study provides a simple and effective method for the establishment of LDH composite UF membrane with excellent performance in oil-water separation, which possesses a great potential for high concentration emulsifying wastewater treatment.