Mussel inspired fabrication of novel superhydrophobic and superoleophilic sponge modified using a high density of nanoaggregates at low concentration of dopamine
PDA nanoaggregates can be formed at ultra high concentrations of dopamine (DA, 8 mg mL 1) promoting application of DA/PDA chemistry in material modification; however, polydopamine (PDA) film also is formed at such concentrations. To achieve a high density of PDA nanoaggregates on the material surface at low concentrations of DA, here, a simple strategy was developed and a novel superhydrophobic/superoleophilic sponge with outstanding adsorbency and flame retardancy was fabricated. Two step DA oxidative self polymerization in different media was applied. After the raw melamine sponge (ME) was first coated with PDA film at 0.5 mg mL 1 of DA in mild buffer (Tris HCl, pH 8.5) the resulting PDA film was then applied as "solid reagent" and contributed to formation of a high density of PDA nanoaggregates at 3.0 mg mL 1 of DA in a harsh medium (water/ethanol/ammonium) Covalent grafting of n dodecylthiol (DT, low surface energy molecular) onto PDA nanoaggregates was combined in the second step using the reactivity of PDA. As investigated by scanning electron microscopy (SEM) the as prepared ME/PDA/DT sponge has a 3D hierarchical structure with a high density of nanoaggregates on an interconnected porous sponge network. The size and density of PDA nanoaggregates on the sponge could be easily controlled by adjusting the concentration of ammonia in the second step. The ME/PDA/DT sponge was superhydrophobic (water contact angle of 161.5deg) and superoleophilic (oil contact angle of 0deg) Owing to the high loading of nanoaggregates, highly porous structure, and superhydrophobic property, the ME/PDA/DT sponge possessed outstanding adsorption properties towards oil and organic solvents, including high adsorption capacity (weight gains ranged from 6632% to 15112% fast adsorption kinetics (reaching adsorption capacity in 30 seconds) and good reusability (no obvious decrease of adsorption capacity after ten adsorption/distillation cycles) The ME/PDA/DT sponge exhibited improved flame retardancy compared with the raw melamine sponge, indicating significant potential for oil adsorption and organic solvent clean up with low risk of fire and explosion.