How the absorption works.
The news moves fast these days, so you can be forgiven for being a little fuzzy about the Deepwater Horizon episode. Here’s a recap: On 20 April 2010, while drilling in the Gulf of Mexico off the coast of Louisiana, an explosion on the off-shore rig killed 11 crewmen and sank the rig, leaving the well gushing at the seabed and causing the largest offshore oil spill in U.S. history.
Forgotten by many, remnants of its destruction still remain in the Gulf in the form of crude oil dispersed in the water and mixed in with the sand – along with the dispersant Corexit, which is now considered a toxic substance.
Here’s how a new plastics application might assist with the ongoing cleanup: researchers at Texas A&M University have developed a non-toxic sequestering agent-iron oxide nanoparticles coated in a polymer mesh that can hold up to 10 times their weight in crude oil – a material that can safely soak up leftover oil, from both the Deepwater Horizon spill and elsewhere, that isn’t captured using conventional mechanical means.
As reported in the ACS Nano scientific journal, the nanoparticles consist of an iron oxide core surrounded by a shell of polymeric material – a simple poly(acrylic acid)-block-polystyrene that possesses both hydrophilic (poly(acrylic acid)) and hydrophobic (polystyrene) groups. This amphiphilic copolymer interacts with both the aliphatic hydrocarbons and aromatic components present in crude oil. Cross-linking the polymer makes the shell more stable in aqueous environments while maintaining the crude oil loading potential.
To simulate an actual oil spill, the Texas A&M team weathered a sample of crude oil to match the conditions of the Deepwater Horizon spill. When the nanoparticles were dropped in the oil-water mixture, they immediately changed color from light tan to black as they soaked up the oil. It gets better: When the nanoparticles were full they floated to the top, making for easy recovery by a conventional magnet, not only from a test vial but also in the ocean. A magnet was held to the side of the vial, nanoparticles collected at the glass, and the water was poured off, leaving the crude oil behind inside of the particles.
Great, but how do you get the oil out? Sonication in ethanol releases the oil from the swollen polymer matrix, causing the nanoparticles to return to a light tan. And although spectroscopic changes were observed after washing, the nanoparticles absorbed the same amount of oil during a second trial. In other words, the system is completely reusable. The next step? Creating an enhanced version that’s biodegradable; as it stands, the existing particles could pose a threat if not collected once they’ve accomplished their duties.
But give the Texas A&M team some time – according to Karen Wooley, the principal investigator of the work, the project is still in the early stages. “But the fact that [our nanoparticle system] can capture 10 times its weight in crude oil is such a promising first result that I think they have significant potential,” she said.
Call it a small polymer mesh silver lining to the Deepwater Horizon tragedy.