Hierarchically-structured ratchet skimmer with superhydrophilicity for continuous recovery of high-viscosity oil

Oil spill accidents have series environmental and economic impacts, increasing the demand for efficient technologies to recover oil from contaminated waters. In this study, a hierarchically structured ratchet surface with superhydrophilicity was presented as a novel oil skimming mechanism for the recovery of high-viscosity oil, particularly low-sulfur fuel oil (LSFO), which has recently been used as marine fuel in open water environments. The interaction between the superhydrophilic ratchet and oil provides favorable conditions for oil retention at the water surface. The hierarchical structure minimizes contact between oil and the skimmer surface, allowing separation without a scraper, even at higher speeds. In addition, the ratchet skimmer generates a water surface flow near the skimmer, driving oil to the drum and improving skimming performance. The skimmer achieved a recovery efficiency of almost 100 % under various experimental conditions with an LSFO viscosity of up to 12,000 cSt.