Although we've seen many materials designed for removing oil spills from water, many of them are single-use, ultimately ending up in landfills. Now, however, scientists have created an oil-absorbing sponge that can be used over and over again.
Developed by Vikas Nandwana and Vinayak Dravid from Northwestern University, the actual sponge itself is much like any other. The secret lies in a thin coating that's applied to it, known as an OHM (oleophilic hydrophobic magnetic) nanocomposite slurry. It's made up of magnetic nanostructures, on a carbon-based substrate.
That substrate is both oleophilic and hydrophobic, meaning (respectively) that it attracts oil and repels water. As a result, the sponge can soak up over 30 times its weight in oil, without also filling up on water. That oil can subsequently be squeezed out for safe disposal or reuse, leaving the sponge ready to take up more.
Additionally, the magnetic aspect of the coating allows the sponge to be moved around on the water's surface via an external magnetic field. This means that a large ship-mounted electromagnet, like those seen at auto wrecking yards, could be used to deploy, retrieve and "steer" batches of the sponges at oil spill sites.
What's more, when an external radio signal is applied to the sponge, it's absorbed by the magnetic nanostructures, causing them to heat up to around 60 ºC (140 ºF). This in turn helps the sponge to release its oil payload, when squeezing alone isn't enough.
"Our sponge works effectively in diverse and extreme aquatic conditions that have different pH and salinity levels," says the first author Dr. Vikas Nandwana.
Down the road, the technology could conceivably be adapted to selectively soak up and release other waterborne pollutants, such as dissolved nutrients from agricultural runoff or sewage.
"We believe we can address a giga-ton problem with a nanoscale solution." says Dravid.