Novel approach for rapid oil/water separation through superhydrophobic/ superoleophilic zinc stearate coated polyurethane sponges

Regarding the indispensable risk management of hazardous accidental releases through oil production and its transportation, spongy absorbents have recently gained wide attention as one of the most effective oil spill cleanup techniques to accumulate the oil in the bulk medium and effectively remove the oil pollution. In this study, a superhydrophobic/superoleophilic novel spongy absorbent has been developed. It is composed of a polyurethane sponge coated with zinc stearate (which is first ever introduced as a superhydrophobic material) and phenol-formaldehyde resin by the dip-coating method, providing both the necessary roughness and chemical hydrophobicity features simultaneously. Characterization by FTIR, SEM, and EDX mapping results showed that the zinc stearate was uniformly dip-coated throughout the polyurethane to roughen the surface; this occurred as the result of the strong chelating bonds formed between the carboxylates and Zn atoms on the surface. However, no significant change happened after immersing this product in acidic and basic solutions. The water contact angle measurements revealed that the static contact angle increased from 70° ± 2 on the unmodified substrate to 175° ± 2 for the zinc stearate-coated sponge. Interestingly, the dynamic water contact angle was also lower than 10°, sliding ~8°, and shedding ~7°, strongly confirming the excellent superhydrophobicity of the fabricated zinc stearate-coated polyurethane. Finally, the absorption rate and capacity of the unmodified and modified sponges using two different polyurethane densities for treating various oils and solvents demonstrated that the coated polyurethane spongy absorbent was capable of absorbing a wide range of oils and organic solvents in a time range of 30–50 ms and oil capacity range of 6–81 times their weight, depending on the different sponge densities.