Cork treated with lasers is effective and sustainable for cleaning up oil spills, efficiently separating oil from water without using chemical dispersants. Source: SciTechDaily.com
The treated cork can absorb more and uses sunlight to capture oil within minutes.
Oil spills are catastrophic events for ocean environments. They can have long-term effects on fish and sea mammals for many years and cause damage to coastal forests, coral reefs, and the surrounding land. Chemical dispersants are commonly used to break down oil, but they often increase its toxicity in the process.
In 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 utilized laser treatments to change normal cork into an effective tool for dealing with oil spills.
They aimed to create an eco-friendly solution for cleaning up oil using materials with a low carbon footprint, but they ended up choosing cork due to an unexpected discovery.
To remove oil from water, the researchers used cork treated with a fast-pulsing laser technique that removes some oxygen from the material, increasing the relative carbon and making it more water-repellent and oil-attracting. Laser treatment also changes the structure of the cork: When viewed at the nanoscopic level, the material has deep grooves that increase the total surface area of the cork and allow it to capture sunlight and warm the oil, making it easier to collect. Source: Yuchun He
Unintentional Discoveries Leading to Environmentally Friendly Solutions
“In a different laser experiment, we accidentally discovered that the properties of the cork processed using a laser changed significantly, gaining superhydrophobic (water-repelling) and superoleophilic (oil-attracting) properties,” author Yuchun He said. “After appropriately adjusting the processing parameters, the surface of the cork became very dark, which made us realize that it might be an excellent material for photothermal conversion.”
“Combining these results with the eco-friendly, recyclable advantages of cork, we thought of using it for marine oil spill cleanup,” author Kai Yin said. “To our knowledge, no one else has tried using cork for cleaning up marine oil spills.”
Cork comes from the bark of cork oak trees, which can live for hundreds of years. These trees can be harvested about every seven years, making cork a renewable material. When the bark is removed, the trees increase their biological activity to replace it and enhance their carbon storage, so harvesting cork helps reduce carbon emissions.
Improvements in Technology and Experiments
The researchers tested different forms of fast-pulsing laser treatment to achieve the best balance of characteristics in the cork that can be attained at a low cost. They closely analyzed nanoscopic structural changes and measured the ratio of oxygen and carbon in the material, changes in the angles at which water and oil come into contact with the surface, and the material’s light wave absorption, reflection, and emission across the spectrum to determine its durability after multiple cycles of heating and cooling.
The laser processing gives cork the ability to heat up quickly in the sun. The deep grooves also increase the surface area exposed to sunlight, so the cork can be warmed by just a little sunlight in 10-15 seconds. This energy is used to heat up spilled oil, lowering its viscosity and making it easier to collect. In experiments, the laser-treated cork collected oil out of water within 2 minutes.
The laser treatments not only improve oil absorption, but also prevent water from getting in.
Practical Applications and Future Prospects
“When the cork undergoes a fast-pulsing laser treatment, its surface microstructure becomes rougher,” Yin said. “This micro- to nano-level roughness enhances hydrophobicity.”
As a result, the cork collects the oil without absorbing water, so the oil can be extracted from the cork and possibly even reused.
“Oil recovery is a complex and systematic task, and participating in oil recovery throughout its entire life cycle is our goal,” Yuchun He said. “The next step is to prepare electrothermal materials using polyurethane foam as the skeleton for oil adsorption, combining photothermal and electrothermal techniques to form an all-weather oil recovery system.”
Reference: “Femtosecond laser structured black superhydrophobic cork for efficient solar-driven cleanup of crude oil” by Yuchun He, Kai Yin, Lingxiao Wang, Tingni Wu, Yu Chen, and Christopher J. Arnusch, 23 April 2024, Applied Physics Letters.
DOI: 10.1063/5.0199291
