Bionic material cleans oil polluted water

oil adsorption

The leaf of the floating fern Salvinia adsorbs crude oil in a matter of seconds. © W. Barthlott, M. Mail/ University of Bonn

If oil gets into lakes and rivers, it endangers the ecosystems there and at the same time contaminates potential drinking water. A chemical-free method copied from nature, with which oil contamination can be removed from the water, can help. This is made possible by a textile with a water-repellent surface to which the oil binds by adhesion. The surface then transports the accumulated crude oil to the appropriate collection tank as if by itself.

When the Deepwater Horizon oil rig exploded in the Gulf of Mexico in 2010, dramatic images went around the world. Dead seabirds covered in pitch black, dead dolphins washed up and an oil slick bigger than Saarland. The rapidly spreading oil spill could hardly be contained at the time and also caused lasting damage to unique ecosystems in the Caribbean and on the south coast of the USA. But even beyond such major catastrophes, leaking oil can have serious consequences for bodies of water and banks. Even small amounts of oil spread rapidly over large areas as a thin, greasy film, endangering animals and plants as well as drinking water resources.

operating principle
Functional principle of the oil adsorber copied from the floating fern. © W. Barthlott, M. Mail/ University of Bonn

Method is copied from nature

A method developed by researchers led by Wilhelm Barthlott from the University of Bonn could help. Because it can also remove minor oil contamination and is also suitable for use in inland waterways. It is based on the physical principle of adsorption, which the researchers copied from nature. Barthlott is known as the discoverer of the so-called lotus effect. A few years ago, he and his team at the time discovered that rough microstructures on the leaf surface of a lotus flower allow drops of water to roll off immediately, taking dirt particles directly with them. In the meantime, this effect has become indispensable in industry.

Plant structures also play a decisive role in the new type of oil absorber. In search of the optimal surface structure for their "oil catcher", Barthlott and his colleagues tested various types of plants for their oil-adsorbing properties. In contrast to absorption, in adsorption the oil is not absorbed into the interior of the plant, but only deposited on its surface. The floating fern Salvinia molesta succeeds best in this, as the experiments showed. In the next step, the researchers transferred the complex surface structure of the fern to suitable functional textiles and thus developed their "bionic oil adsorber".

Industrial production in the near future

In practice, the oil adsorber works as follows: Oil-absorbing textiles are attached to a floating collection container in strips six centimeters wide. One end of the strips protrudes into the container, the other into the surrounding, contaminated water. "In this submerged part there is initially an air film, which is then replaced by adsorbed oil and transported to the storage container," the scientists explain. Due to the adhesion and the transport along the surface, the leaked oil migrates into the container "as if by itself" - i.e. without any energy expenditure. "It can then be emptied and the oil can even be reused if necessary," reports Barthlott.

The process is not only energy-efficient, but also very powerful. The research team's tests showed that even a comparatively small prototype can collect up to three liters of oil per hour from the surface of a body of water. How quickly the bionic oil adsorber cleans a polluted body of water also depends on the nature of the oil. For example, diesel can be transported 50 times faster than engine oil due to its lower viscosity, explains Barthlott. In addition to using the technology in polluted inland waters, use in shipping or in industrial plants is also conceivable. Barthlott estimates that the bionic oil adsorber can soon be industrially produced due to the convincing test results.

Source: German Federal Environmental Foundation (DBU); Specialist article: Philosophical Transactions of the Royal Society A, doi: 10.1098/rsta.2019.0447

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