Graphene-based melamine sponges with reverse wettability for oil/water separation through absorption and filtration

To achieve oil/water separation using both absorption and filtration regardless of the oil/water density relationship, the super-hydrophilic/underwater super-oleophobic graphene oxide coated melamine sponge ([email protected]) and super-hydrophobic/super-oleophilic reduced graphene oxide coated melamine sponge ([email protected]) were prepared via dip-coating of graphene oxide (GO) sheets onto melamine sponge (MS) and subsequent chemical reduction, respectively. The structures of the [email protected] and [email protected] were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, and X-ray diffraction (XRD). Both [email protected] and [email protected] can preserve their original wettability in harsh environments containing acidic, alkaline, saline, and hot waters. The [email protected] and [email protected] show excellent capability for selective absorption of water and oil respectively, with high capacities of 72.3–136.5 g g−1 and excellent recyclability. The compressed [email protected] and [email protected] also exhibit high separation efficiency of about 99% and ultra-high permeation flux above 1.62 × 105 L m−2 h−1 for separating different oil/water mixtures containing light and heavy oils through filtration driven by gravity, respectively. Furthermore, a bidirectional separation setup assembled with the compressed [email protected] and [email protected] was constructed, which demonstrates high efficiency for continuously separating different oil/water mixtures of any oil density.