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Cactus-inspired micro needles have been used to remove tiny oil droplets from water with almost 100 percent efficiency.
Researchers at the Chinese Academy of Sciences in Beijing have developed a technique for hovering up micron-sized oil droplets using an array of cones made from oil-loving materials.
The biomimicking array can operate continuously, without cleaning or refreshing, and was able to remove up to 98.9 percent of the oil from water samples, according to a paper published in
Nature Communications on 6 August. "Micron-sized oil droplets in water and micron-sized water droplets in air are similar," write the authors. "So we can move the cactus-inspired system underwater."
When oil and water have cleanly separated, it is relatively straightforward to separate the layer of oil from the water.
However, when the oil is dispersed throughout the water in tiny droplets, it is much more difficult.
Since the Deepwater Horizon oil spill in 2010, several teams have investigated methods of separating mixtures of oil and water, primarily through the use of membranes that allow water but not oil to pass through.
With the micro needle solution, oil droplets accumulate at the tips of the needles and then travel up the cone to the base, where they form much larger droplets that can then be sucked away.
The droplets move under their own steam because their curvature is greater at the side nearer the tip than on the side nearer the base. This creates a force imbalance that drives the droplets up the cone.
Rough needles were found to be 2.5 times more efficient than smooth needles, and taller needles in higher densities were more efficient than shorter, sparse needles. This is likely because the number of surfaces for the oil to land on is greater when the needles are tall and dense as opposed to short and sparse.
Oils like gasoline and petroleum ether were successfully separated from water. Cones made from a range of oil-loving materials, including rubbed polystyrene, were found to work.
Earlier this year, researchers at the Chinese Academy of Sciences, led by Lei Jiang, a co-author of the oil study, found that the cactus Optunia microdasys removes water from the air using its needles -- a discovery that inspired this innovation.
This article was originally published by WIRED UK
