Oil spills are devastating disasters for marine ecosystems, with lasting consequences on aquatic and marine wildlife, as well as coastal ecosystems like forests and coral reefs. To counteract this, chemical dispersants are commonly used to break down the oil, but this method often increases its toxicity.
In a study published in
Applied Physics Letters by
AIP Publishing, researchers from Central South University, Huazhong University of Science and Technology, and Ben-Gurion University of the Negev have used laser treatments to transform ordinary cork into a powerful tool for addressing oil spills.
Their primary goal was to develop an effective and environmentally friendly oil cleanup solution, focusing on materials with low environmental impact. However, their choice to use cork was the result of a serendipitous discovery. "While conducting a different laser experiment, we accidentally found that the wettability of the laser-treated cork changed significantly, acquiring superhydrophobic (water-repelling) and superoleophilic (oil-attracting) properties," said author Yuchun He. "After properly adjusting the treatment parameters, the cork's surface turned very dark, which made us realize it could be an excellent material for photothermal conversion."
"Combining these findings with the ecological and recyclable benefits of cork, we thought of using it to clean up oil spills at sea," added author Kai Yin. "To our knowledge, no one else has tried using cork for cleaning up oil spills at sea."
(a) Diagram of the optical path of femtosecond laser treatment;
(b) diagrams of virgin cork and treated cork and their enlarged structural schematics;
(c) optical photos of virgin cork and treated cork and the behavior of light on their surfaces, with a 5 mm scale bar;
(d) diagram of the real application scenario of treated cork. Cork comes from the bark of cork oaks, trees that can live for several centuries. These trees can be harvested about every seven years, making them a renewable resource. When their bark is removed, these trees intensify their biological activity to regenerate it, thereby increasing their carbon storage capacity and helping to reduce carbon emissions.
Researchers explored different variations of rapid pulse laser treatment to achieve an optimal balance of cork features while minimizing costs. Their study involved a detailed analysis of structural changes at the nanoscopic scale, measuring the oxygen and carbon ratio in the material, evaluating changes in contact angles between water, oil, and cork surface, as well as studying the absorption, reflection, and emission of light across the spectrum, in an effort to determine the material's durability after several heating and cooling cycles.
The photothermal characteristics obtained from laser treatment allow the cork to heat up quickly in sunlight. Deeper grooves increase the surface area exposed to the sun, enabling the cork to heat up in just 10 to 15 seconds with minimal solar exposure. This energy is then used to warm the spilled oil, reducing its viscosity and facilitating its collection. During the experiments, the laser-treated cork successfully recovered floating oil at sea in less than 2 minutes.
Laser treatments not only enhance oil absorption but also keep water at bay. "When cork undergoes rapid pulse laser treatment, its surface microstructure becomes rougher," said Yin. "This micro to nano-level roughness increases hydrophobicity." As a result, the cork absorbs oil without absorbing water, allowing the extracted oil to be potentially reused.
"Oil recovery is a complex and systematic task, and participating in the oil recovery throughout its lifecycle is our goal," stated Yuchun He. "The next step involves preparing electrothermal materials using polyurethane foam as a skeleton for oil adsorption, combining photothermal and electrothermal techniques to create an all-season oil recovery system."
Article author: Cédric DEPOND