Fabrication and characterization of superhydrophobic melamine foam for effective separation of immiscible and emulsified oil/water mixtures

Frequent oil spills and oily wastewater discharge have caused serious damage to the ecological environment, which make it urgent to address these challenges. Herein, we report an effective strategy and low-cost method to transform commercially available melamine foams into superhydrophobic/superoleophilic absorbents, which has a high separation ability for both oil-water mixtures and emulsions. Our approach involves the co-deposition of tannic acid and 3-aminopropyltriethoxysilane on the foam surface to form a hierarchical structure, followed by the covalent grafting of palmitic acid with low surface energy onto the foam backbones via acylation. The resulting foam maintained a cross-linked porous structure with a water contact angle of 153° and a sliding angle of 7°, exhibiting a high degree of water repellency. Absorption experiments with chloroform and engine oil showed that the foam has high absorption capacity, reaching 99.2 and 172.8 times its own weight, respectively, and the foam still retains excellent elasticity after 1000 compression cycles. In addition, the superhydrophobic foam has a high demulsification ability to oil-in-water emulsions by repeated compression and violent stirring, and its separation ability for toluene-in-water emulsions was up to 99.25%. Based on these results, the superhydrophobic foam has significant potential for large-scale oil spill cleanup and wastewater purification.