Hydrophobic melamine sponge prepared by direct fluorination for efficient separation of emulsions

• Direct fluorination was used to make the surface of a melamine sponge hydrophobic. • 3D structure of melamine sponge was maintained during direct fluorination. • Fluorinated sponge was able to separate surfactant-stabilized water-in-oil emulsions. • Fluorinated sponge has excellent mechanical properties and recyclability. • Fluorinated sponge is promising absorbent for industrial purification and separation. Hydrophobic polymer sponges have recently attracted attention as promising absorbents for oil-water separation due to their excellent absorption ability and high selectivity. Many hydrophobic modification methods have been reported for sponges, but rapid and easy methods applicable on a large scale still requires a lot of research. In this study, direct fluorination was used to make the surface of an amphiphilic melamine sponge (MS) hydrophobic. Fluorine functional groups were effectively introduced on the surface of the melamine sponge (MS) while maintaining the three-dimensional structure, and this was accomplished with a low fluorine partial pressure ratio (F 2 :N 2 = 0.5:9.5). Fluorinated MS (F-MS) showed an oil absorption capacity of 79 to 180 times its own weight for various oil/organic solvents and maintained 97.8% of the original adsorption capacity after 30 cycles of immersion-squeezing-heating. More importantly, F-MS showed a 95% higher water rejection coefficient for surfactant-stabilized water-in-oil emulsions, and still showed an excellent separation efficiency after 14 days. Since F-MS, which was hydrophobically modified with direct fluorination, has excellent oil/water separation capacity, recyclability, and long-term stability, it is a very promising absorbent for separation purification in industrial applications.