Facile Preparation of Hydrophobic Melamine Sponges using Naturally Derived Urushiol for Efficient Oil/Water Separation

In this work, hydrophobic sponges for highly efficient oil/water separation and oil absorption were fabricated by a simple, eco-friendly, economical, and scalable dip-coating of hydrophilic melamine sponges in urushiol (a naturally occurring small compound) solution. Because of the unique catechol group and a long alkyl side chain with unsaturated double bonds, urushiol molecules easily adhered on the sponge wall surface and self-polymerized to form a thin hydrophobic coating layer with the assistance of heat treatment. The urushiol-modified melamine sponge (UMS) displayed a water contact angle of ∼139o and a 3D highly porous structure, so it could effectively separate oil from dynamic oil/water mixtures. The separation flux of n-hexane from an n-hexane/water mixture was as high as 18,356 ± 2200 L·m–2·h–1·bar–1. It could quickly absorb various oils and common organic solvents with an absorption capacity of up to 181 g·g–1 and had excellent recyclability. UMS also displayed robust mechanical stability, flexibility, elasticity, and thermal stability. Therefore, the facile preparation process, low cost, and superior oil separation/absorption would endow UMS with high potential when dealing with oily wastewater.