3D superhydrophobic sponge with a novel compression strategy for effective water-in-oil emulsion separation and its separation mechanism

Oil/water mixtures are easily converted into microemulsions with high stability and complex structures under the action of surfactant, causing great difficulties for effective separation. In this paper, we report a 3D porous melamine sponge with superhydrophobic and superoleophilic properties via a facile 1,4-conjugate addition reaction between amine and acrylate groups for coating nano-complex on the sponge surface and subsequently covalent modification with amine-functionalized long-chain alkane for decrease the surface energy. In order to satisfy the requirement of pore sizes in emulsion separation, a novel and controllable approach has been explored to control the pore sizes and 3D porous structure of the resultant sponge by the mechanical compression strategy. Notably, when the emulsified oil/water mixtures were poured into the modified sponge with 90% compression degree of its original volume, the demulsification occurred immediately and then the oil phase passed through the sponge quickly, while water droplets were interrupted in the tortuous pore channels. Combined with the special wettability and the novel pore sizes tuning strategy, the resulting sponges can effectively separate a wide range of surfactant-stabilized water-in-oil emulsions with fast permeation flux of 32,500 ± 2000 L m −2  h −1  bar −1 under the action of gravity and extremely high oil purity (>99.97%). It is expected that the superhydrophobic sponge with the novel compression approach can provide a general strategy for 3D porous materials used for effective separation of emulsified oil/water emulsions.