Lotus- and Mussel-Inspired PDA–PET/PTFE Janus Membrane: Toward Integrated Separation of Light and Heavy Oils from Water

Current special wetting materials designed for use with oily wastewater are usually classified as either the oil-removing type or the water-removing type, which are unifunctional and limited by the oil density. Inspired by the integrated Janus system of the lotus leaf as well as the mussel-like mollusks adhered to the lotus, we fabricated a Janus polydopamine (PDA)-polyethylene terephthalate/polytetrafluoroethylene (PET/PTFE) membrane by simple immersion and tape-peeling. This membrane shows a lotuslike Janus wettability, self-cleaning effect, and floating property. Furthermore, the Janus membrane can separate light oil (ρ_oil < ρ_water)/water mixtures with the superhydrophilic side facing upward, while heavy oil (ρ_oil > ρ_water)/water mixtures are separated with the hydrophobic side facing upward. The separation efficiency is outstanding even after 10 repeats (>99.10%). By aid of drainage of acetone, the separation process has avoided the use of external pressure. Moreover, integrated separations of oil-in-water and water-in-oil emulsions were achieved with high efficiency. This simply prepared PDA-PET/PTFE Janus membrane has realized an integrated separation system, overcoming the monotony of traditional special wettability separation membrane and extending the bionics field into oily wastewater treatment.