Fabrication of superhydrophobic melamine sponge composite sorbent in supercritical carbon dioxide atmosphere for selective and effective oil removal from water

In this study, both the modification of activated halloysite nanotube (HNT) with methyltriethoxysilane (METES) and the fabrication of durable, superhydrophobic (water contact angle: 153.0°) and superoleophilic (oil contact angle: 0°) melamine sponge (MS)-HNT-METES sorbent material (MS-METES) were achieved in supercritical carbon dioxide (scCO2) atmosphere. For the coating of MS with clay mineral and METES through sol-gel reaction in scCO2, optimal process conditions were determined to be pressure difference of 60 bars at 35°C, solvent/METES mass ratio of 7.5, METES/MS mass ratio of 10, and degas time of 400 s. Successful preparation of MS-METES was proven by XPS, FTIR, 29Si-MAS NMR, SEM, and contact angle measurements. MS-METES displayed excellent sorption capacity for various petroleum products, oils, and organic solvents (49.6-122.4 g/g), remarkable oil-water separation efficiency (99.1%, for continuous separation technique), high selectivity for oil/organic solvent in acidic, salty, and alkaline solution conditions, good reusability, chemical stability and robustness, and outstanding flexibility and mechanical stability. We believe that the innovative process used in this study will have great potential to be used by researchers in the direct fabrication of new superhydrophobic and superoleophilic sorbent materials for the selective removal of oil and organic solvent spills from water.