One-Step Preparation of Highly Hydrophobic and Oleophilic Melamine Sponges via Metal-Ion-Induced Wettability Transition

Hydrophobic and oleophilic absorbent materials have received wide attention in recent years for potential applications in pollutant removal from accidental spills of oil or organic chemicals. In this work, we report a metal-ion-induced hydrophobic melamine sponge (MII-HMS) prepared by a one-step solution immersion process. The commercial melamine sponge (intrinsically superhydrophilic with a water contact angle of ∼0°) is immersed in an aqueous solution of transition metal ions (e.g., FeCl₃, Fe­(NO₃)₃, Zn­(NO₃)₂, Ni­(NO₃)₂, and Co­(NO₃)₂) for a short period, followed by drying. This simple process renders the transition of the superhydrophilic melamine sponge to become highly hydrophobic (a water contact angle of ∼130°). Results from X-ray photoelectron spectroscopy and infrared spectroscopy suggest that the unprecedented transition is likely due to the formation of metal complexes during immersion. The MII-HMS is also oleophilic, exhibiting excellent oil absorption capabilities, ∼71–157 times of its weight, for a wide range of oils and organic solvents. Our work offers a simple, scalable, and economical approach to fabricate highly efficient absorbent materials for potential applications in oil spill recovery and environmental remediation.