Preparation of superhydrophobic MnO2 nanorod-Fe3O4 nanoparticle functionalized melamine sponges for oil–water separation

In this work, novel MnO₂–Fe₃O₄/melamine (MA) sponges have been prepared for oil–water separation. First, MnO₂ nanorods were synthesized by a hydrothermal method and their morphology could be controlled by different reaction conditions. Next, the as-prepared MnO₂ nanorods were used alone or in combination with Fe₃O₄ nanoparticles to obtain hydrophobic MA sponges by surface modification with the assistance of silane coupling agents and/or Sylgard 184 adhesive. The realization of the high roughness and the coating with a low surface energy material for surface-modified MA sponges were mainly confirmed by SEM and FTIR, respectively, which were two key factors for the enhancement of hydrophobicity. All investigated MnO₂/MA and Fe₃O₄/MA sponges were hydrophobic but with the water contact angles (WCAs) lower than 150°, while the WCAs of MnO₂–Fe₃O₄/MA sponges could reach or exceed 150° under suitable preparation conditions achieving superhydrophobicity, which was attributed to the improved roughness. Both MnO₂/MA and MnO₂–Fe₃O₄/MA sponges had good oil–water separation ability by direct adsorption and gravity filtration, and their adsorption capacities for different oils were measured to be 37–50 g g⁻¹ and 35–67 g g⁻¹, respectively. Additionally, the saturation magnetization of the MnO₂–Fe₃O₄/MA sponge could reach as high as 17.3 emu g⁻¹, which is beneficial for the magnetic control operation during oil–water separation application.