Nature-inspired textiles remove oil from water

Researchers from the University of Bonn, RWTH Aachen University and textiles supplier Heimbach have developed a new technology for removing oil from water sources.

The team created textiles with special surface properties that passively skim off the oil and move it into a floating container, using surfaces from the plant kingdom as a model. Their study has been published in the journal Philosophical Transactions of the Royal Society A and their plant model is demonstrated in the video clip below.

The clip shows a pipette from which dark-coloured crude oil drips into a glass of water. Then a researcher holds a green leaf against the spot. Within a matter of seconds the leaf sucks the oil from the surface of the water, leaving not even a trace behind.

The star of the movie, the small green leaf, comes from the floating fern Salvinia. The special abilities of its leaves make it highly interesting for scientists, because they are extremely hydrophobic: when submerged, they wrap themselves in an air jacket and remain completely dry. Researchers call this behaviour ‘superhydrophobic’, or extremely water repellent; however, the Salvinia surface also loves oil, which is in a way a flip side of superhydrophobia.

“This allows the leaves to transport an oil film on their surface,” explained Prof Dr Wilhelm Barthlott from the University of Bonn. “And we have also been able to transfer this property to technically producible surfaces, such as textiles.”

Such superhydrophobic substances can then, for instance, be used to remove oil films from water surfaces efficiently and without the use of chemicals. However, unlike other materials that have been used for this purpose so far, they do not absorb the oil.

“Instead, it travels along the surface of the fabric, moved forward solely by its adhesive forces,” said Prof Dr Barthlott. “For example, in the laboratory we hung such fabric tapes over the edge of a container floating on the water. Within a short time they had almost completely removed the oil from the water surface and transported it into the container.”

Gravity provides the power; the bottom of the container must therefore be below the water surface with the oil film. “The oil is then completely skimmed off — as if using an automatic skimming spoon for meat stock,” Prof Dr Barthlott said.

This also makes superhydrophobic textiles interesting for environmental technology, promising a new approach to solving the acute environmental problem of increasing oil spills on water bodies. The new process does not require the use of chemicals and is different to conventional binding agents, which simply absorb the oil and can then usually only be burned later.

“The oil skimmed into the floating container is so clean that it can be re-used,” said Prof Dr Barthlott.

The procedure is not intended for large-scale oil disasters such as those that occur after a tanker accident. But particularly small contaminations, such as engine oil from cars or ships, heating oil or leaks, are a pressing problem.

“Even minor quantities become a danger to the ecosystem, especially in stagnant or slow-flowing waters,” said Prof Dr Barthlott. This is where he sees the major application potential of the new method, for which a patent has been filed by the University of Bonn.

Image caption: A drop of crude oil on a water surface is adsorbed within seconds by a leaf of the floating fern Salvinia and pulled from the water. Image ©W Barthlott, M Mail/Uni Bonn.

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