Superwettable Janus nylon membrane for multifunctional emulsion separation

With the increasing environmental pollution caused by oily wastewater and oil spill accidents, many superwettable materials have been prepared and applied for the separation of oil-water mixtures. However, the fabrication of superwettable materials for multifunctional water purification including oil-in-water and water-in-oil emulsion separation, dyes degradation and heavy metal ions removal still remains challenging. Herein, we propose a facile method to fabricate a superwettable Janus nylon membrane through in situ generation of silver (Ag) particles immobilized by polydopamine and asymmetric chemical modification with dodecanethiol (NDM) and l-cysteine (L-cys) on the positive and negative surfaces, respectively. The positive surface modified by NDM exhibited superhydrophobicity and superoleophilicity, and the negative surface chemically bonded with L-cys possessed opposite wettability with superhydrophilicity and underwater superoleophobicity. The positive and negative surfaces of the Janus membrane were respectively applied for the separations of water-in-oil emulsions and oil-in-water emulsions, and the separation efficiencies all reached above 99%, also demonstrating great reusability and wide adaptability. In addition, the Janus membrane presented not only outstanding performance of degrading methylene blue (MB) with high efficiency above 97.3%, but also excellent capability of absorbing heavy metal ions in the process of emulsion separation. The fabrication processes are facile, mild, and no special equipment is involved, and our findings conceivably provided a new strategy to fabricate superwettable Janus membrane for multifunctional emulsion separation and wastewater purification.