A bioinspired strategy to construct dual-superlyophobic PPMB membrane for switchable oil/water separation

Separation membranes with under-liquid dual-superlyophobicity have attractive features owing to their switchable separation of oil/water emulsions and mixtures. However, due to the thermodynamic contradiction, there are great challenges in the preparation of underwater superoleophobic and underoil superhydrophobic membranes. Herein, we report a bioinspired accurate-deposition strategy to fabricate the under-liquid dual-superlyphobic polypropylene melt blown (PPMB) membrane integrated with photocatalysis self-cleaning property. For the first time, we found that UV oxidized gallic acid (UGA) can react with polyethyleneimine (PEI) rapidly to form unique coral-like three-dimensional micro-/nanoscale structures, which have a vital effect on the membrane under-liquid dual-superlyophobicity. Meanwhile, using UGA/PEI coating as an intermediate adhesive layer, a novel, green and fast coating method for tightly anchoring titanate nanotubes (TNTs) on the PPMB membranes was developed. Only driven by gravity, the membrane showed extraordinary ability for switchable oil/water mixtures separation with high fluxes above 12,000 L m−2 h−1, and high separation efficiencies all greater than 99.9%. For switchable separation of emulsions, the as-prepared membrane still performed a high permeating flux above 2500 L m−2 h−1 under gravity. Moreover, when the membrane was fouled by continuous surfactant-stabilized emulsions, the photocatalysis self-cleaning property made the regeneration of the membrane green and environmentally friendly.