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Capillary Skimming of Floating Microplastics via a Water‐Bridged Ratchet
Summary
Scientists demonstrated a novel removal technique for floating microplastics using capillary forces: a rising hydrophilic ratchet surface causes floating particles to self-attach via surface tension effects (the Cheerios effect), allowing them to be physically lifted from the water surface without the clogging problems that plague conventional filters. The method worked on particles ranging from 1 to 4 mm across nearly all common plastic types, and a small robotic prototype validated the concept for potential marine cleanup applications.
Floating microplastics (MPs) have recently become a major concern in marine pollution; however, current filter-based technology is hardly effective for directly removing such MPs from the water surface because of specific mesh size and clogging issues. This paper introduces a new skimming concept for removing floating MPs utilizing capillary force mediated by the elevation of a hydrophilic ratchet at the air-water interface. MPs floating near the ratchet surface are spontaneously forced toward the ratchet with a concave water meniscus, driven by the Cheerios effect. The MPs can then be skimmed and temporarily held by the deforming concave water meniscus as the ratchet rises. Here, it is found that the stability of the water bridge plays a crucial role in skimming success because it provides capillary adhesion between the MP and the ratchet. The proposed capillary skimming method is observed to be effective across nearly all types of floating MPs, ranging in size from 1 to 4 mm, and with densities varying from 0.02 to 0.97 g cm- 3, which is also demonstrated by a prototype of marine robot cleaner.