The team of researchers at Northwestern University have developed a highly porous smart sponge that selectively soaks up oil in water.
The sponge, which absorbs more than 30 times its weight in oil, could be used to inexpensively and efficiently clean up oil spills without harming marine life.
The research also found that after squeezing the oil out of the sponge, it can be reused many dozens of times without losing its effectiveness.
The lead researcher Vinayak Dravid, Professor of Materials Science and Engineering at Northwestern’s McCormick School of Engineering, said that even though “many” spills are small, they can be “devastating” for the “environment, human health, and economy”.
“Our sponge can remediate these spills in a more economic, efficient and eco-friendly manner than any of the current state-of-the-art solutions,” he said.
Clean-ups after oil spills are not only expensive, but are very complicated and often harm marine life, risking further damage to the environment.
Current solutions include burning the oil by using chemical dispersants to break it down into very small droplets, skimming oil floating on top of water or absorbing it with expensive, unrecyclable sorbents.
Vikas Nandwana, a senior research associate in Dravid’s laboratory, is the paper’s first author.
“Each approach has its own drawbacks and none are sustainable solutions,” Nandwana said.
“Burning increases carbon emissions and dispersants are terribly harmful for marine wildlife. Skimmers don’t work in rough waters or with thin layers of oil. And sorbents are not only expensive, but they generate a huge amount of physical waste — similar to the diaper landfill issue.”
This new sponge bypasses these challenges by selectively absorbing oil and leaving clean water and unaffected marine life behind.
The secret lies in a nanocomposite coating of magnetic nanostructures and a carbon-based substrate that is oleophilic (attracts oil), hydrophobic (resists water) and magnetic.
The nanocomposite’s nanoporous 3D structure selectively interacts with and binds to the oil molecules, capturing and storing the oil until it is squeezed out. The magnetic nanostructures give the smart sponge two additional functionalities: controlled movement in the presence of an external magnetic field and desorption of adsorbed components, such as oil, in a simulated and remote manner.
The OHM (oleophilic hydrophobic magnetic) nanocomposite slurry can be used to coat any cheap, commercially available sponge. The researchers applied a thin coating of the slurry to the sponge, squeezed out the excess and let it dry. The sponge is quickly and easily converted into a smart sponge (or “OHM sponge”) with a selective affinity for oil.
Vinayak and his team tested the OHM sponge with many different types of crude oils of varying density and viscosity.
The OHM sponge consistently absorbed up to 30 times its weight in oil, leaving the water behind. To mimic natural waves, researchers put the OHM sponge on a shaker submerged in water.
Even after vigorous shaking, the sponge released less than 1% of its absorbed oil back into the water.
“Our sponge works effectively in diverse and extreme aquatic conditions that have different pH and salinity levels,” Dravid added. “We believe we can address a giga-ton problem with a nanoscale solution.”
Nandwana emphasised how exciting it is that a sponge can “selectively” remove and recover pollutants.
“We are excited to introduce such smart sponges as an environmental remediation platform for selectively removing and recovering pollutants present in water, soil and air, such as excess nutrients, heavy metal contaminants, VOC/toxins and others,” He added. “The nanostructure coating can be tailored to selectively adsorb (and later desorb) these pollutants.”
The team plans to develop and commercialize OHM technology for environmental clean-up.
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