Schiff-base modified melamine foams: Tuning hydrophobicity and oleophilicity via benzaldehyde derivatives for selective oil adsorption

Abstract

Melamine foam (MF) was chemically modified with various benzaldehyde (BA) derivatives via Schiff-base formation to enhance its hydrophobicity and oleophilicity for oil spill remediation. BA derivatives with nitro, chloro, methyl, or carboxy groups were grafted onto MF through acid-catalyzed condensation with surface amines, forming imine-linked (C=N) structures. SEM showed the foam's porous 3D network remained intact, while FTIR confirmed Schiff-base formation. Water contact angle measurements indicated significantly increased hydrophobicity in all modified foams except the carboxy-substituted variant (CBA-MF), which remained more hydrophilic due to hydrogen bonding. Hydrophobicity trends correlated inversely with substituent electronegativity. Modified MFs showed strong oil selectivity, efficiently absorbing nonpolar oils while repelling water—especially nitrobenzaldehyde-modified MF (NBA-MF), which floated and absorbed oil effectively. Adsorption tests showed high capacities (up to 149 g/g), correlating with surface hydrophobicity. Modified foams were durable, retaining over 90 % adsorption capacity after 10 reuse cycles. Paraffin oil adsorption followed zero-order kinetics, with rates increasing alongside hydrophobicity. Overall, Schiff-base modification successfully transformed MF into a reusable, highly effective sorbent for selective oil recovery in water.