Durable superhydrophobic melamine sponge based on polybenzoxazine and Fe3O4 for oil/water separation

Oil/water separation through superhydrophobic sponges is an important method for oily wastewater and organic solvents pollution treatments, and developing a simple and eco-friendly approach to fabricate superhydrophobic sponge is still very urgent and valuable. In this work, Fe3O4 and bio-benzoxazine based on cardanol and long-chain aliphatic amine were successively loaded on melamine sponge (MS) through a simple dip-coating method, which was thermally cured to obtain superhydrophobic MS. The as-prepared superhydrophobic MS (P15C-O/Fe3O4/MS) not only exhibited high oil absorption capacity from 65.8 to 136.2 times its own weight for various oils and organic solvents, but also showed excellent recyclability with a water contact angle (WCA) of about 149 degrees after 50 absorbing-squeezing cycles and an absorption retention of more than 92% after 100 cycles. Moreover, P15C-O/Fe3O4/MS also possessed outstanding chemical stability, whose WCA almost kept unchanged after touching with strong acid (pH = 1) and alkali (pH = 13) as well as NaCl solutions for 48 h. The outstanding recyclability and stability of P15C-O/Fe3O4/MS were from the stability of polybenzoxazine and strong adhesion between the coating and sponge, due to the formation of coordination interactions between Fe3+ and N, O atoms as well as hydrogen bonds between polybenzoxazine and sponge. In addition, P15C-O/Fe3O4/MS could be used for continuous oil-water separation and driven remotely by a magnetic force. These advantages make P15C-O/Fe3O4/MS a potential candidate for large-area oil-spill cleanup and oily wastewater treatment, especially under some dangerous conditions.