Nontraditional oil sorbents: Hydrophilic sponges with hydrophobic skin layer for efficient oil spill remediation

Advances in the use of porous materials for oil-water separation offer a promising avenue for solving oil spill problems. Conventionally, to realize selective oil absorption, porous sorbents need to be fully hydrophobized with low-surface-energy chemicals. However, such exhaustive hydrophobization brings about problems of excessive chemical consumption, high cost and increased environmental hazards, hindering the practical applications of sorbents. Here, an innovative type of oil sorbent is developed via a facile liquid film-based dip coating technique. Unlike conventional fully-hydrophobized sorbents, only the outmost layer of our sorbent is modified with hydrophobic polydimethylsiloxane (PDMS) coating while the inner part remains hydrophilic, thus achieving 80% reduction in low-surface-energy chemical consumption. The prepared sorbent allows highly selective oil absorption from oil-water mixture, as the hydrophobic skin layer blocks water entrance and the hydrophilic inner part drives oil absorption. More importantly, our sorbent significantly speeds up oil absorption, and compared with conventional hydrophobic sponges, the absorption time is reduced by 36% for absorption of the same mass of crude oil, attributed to the strong capillary absorption of its hydrophilic inner channels. This sorbent also shows larger specific absorption capacity than its fully hydrophobized counterpart. Our study provides a general strategy to develop cost-effective and environmental-benign sorbents with enhanced oil spill absorption performances.