Macropore absorbent with bihydrophilic layers for the recovery of low-sulfur fuel oil

Conventional absorbent pads are widely employed for oil spill cleanup; however, their microporous structures face challenges in absorbing low-sulfur fuel oil (LSFO), especially at lower temperatures when LSFO solidifies owing to its high-viscosity shear stress. In this study, we developed a macroporous absorbent with bihydrophilic layers (MABL), i.e., a central hydrophobic layer sandwiched between two hydrophilic layers, with improved LSFO absorption efficiency. Unlike conventional hydrophobic absorbents, which remain predominantly afloat on the water surface with minimal submersion, the MABL achieves partial submersion owing to the wettability contrast of the bottom and central hydrophobic layers. This configuration ensures that the water surface aligns within the thickness range of MABL. The optimal pore size for LSFO absorption is determined to be 2.8 mm; pores smaller than 2.8 mm hinder LSFO absorption because of high-viscosity shear stress, while larger pores result in easy release of the absorbed LSFO. Notably, as the temperature decreases and LSFO solidifies, the MABL with 2.8-mm pores demonstrates significantly higher LSFO absorption capacity than conventional absorbent pads. Furthermore, a retention capability experiment reveals that the MABL with a pore size of 2.8 mm retains absorbed LSFO effectively under rotational flow in water and high-acceleration vibration in air, demonstrating its stability under dynamic conditions.