Preparation of highly hydrophobic melamine sponge for oil-water separation through copolymerization deposition

The frequent occurrence of petrochemical spills and the uncontrolled discharge of oily industrial wastewater have caused serious water pollution problems. In this study, a novel modified melamine sponge, namely U-HDA@MS, was prepared by a simple, environmentally friendly, and cost-effective method using urushiol, a natural polymer, as the major modifier. The reaction mechanism of the precipitation copolymerization of urushiol and 1,6-hexamethylenediamine (HDA) and the in-situ deposition of the copolymer were investigated by chemical structure and microscopic morphology analyses. It was found that the self-polymerization of urushiol and the copolymerization of urushiol and HDA produced ethanol-insoluble copolymers. Subsequently, the deposition of the copolymers formed a coating with a micro/nano hierarchical structure and a large number of hydrophobic groups on the sponge skeleton, making U-HDA@MS highly hydrophobic and oleophilic. The water contact angle reached 145° without silanization modification, and the absorption capacity for carbon tetrachloride was up to 122 g/g. The outstanding chemical stability of the deposited coating made U-HDA@MS durable in harsh conditions. It maintained stable hydrophobicity and high absorption capacity over a wide pH range. Absorption-squeezing and continuous absorption experiments verified the outstanding reusability and oil-water selectivity of U-HDA@MS. This demonstrates its promising application in oil-water separation and petrochemical spill cleanup.