Superhydrophobic melamine sponge with excellent surface selectivity and fire retardancy for oil absorption

Flexible porous materials have been widely used as precursors for preparing superhydrophobic oil absorbents due to their high capacity and extraordinary recyclability. A final product with multiple characteristics such as superhydrophobicity, fire retardancy, good elasticity, low cost, and environmental friendliness is highly needed for practical applications. In this study, superhydrophobic melamine sponges (SMSs) with the above characteristics were prepared by modifying melamine sponges with polymethylsilsesquioxane via an immersion method. A villiform layer of organosilane was coated on the surface of the melamine fibers and disclosed by scanning electron microscopy. The superhydrophobicity of the sponge with a water contact angle of 156° is due to the increased surface roughness and methyl terminal groups exposed at the interface. Polycondensation reaction between the secondary amine groups on the raw sponge surface and silanol is identified by ATR-FTIR and EDX spectra. The SMS effectively absorbs various organic solvents and oils from water with excellent absorption rate. In addition, it maintains stable superhydrophobicity in extreme environments, including strong acid/alkali conditions, high/low temperatures, and prolonged immersion in organic solvents. Importantly, the SMS retains the intrinsic fire retardancy of the raw melamine sponge. In simulating oil spill environments, the SMS shows good performance in blocking spread of crude oil spill and separating surfactant-free water-in-oil emulsions. These advantages make it a promising material for oily wastewater treatment and oil spill clean-ups.