Wood sponges off oil in water

A sample of the sponge material draws red-dyed oil from a beaker of water. Courtesy: American Chemical Society’s Nano magazine.

Oil spills and industrial discharge can contaminate water with greasy substances. Although it’s true that oil and water don’t mix, separating and recovering each component can still be challenging.

Now, researchers have created sponges made from wood that selectively absorb oil, and then can be squeezed out and used again!

Over the years, scientists have developed numerous techniques to clean up oily water, from gravity separation to burning to bio-remediation. But many of these methods suffer from limitations, such as low efficiency, secondary pollution and high cost.

More recently, researchers have explored 3-D porous materials, such as aerogels or sponges, based on various building blocks including synthetic polymers, silica or cellulose nano fibres. But these are often difficult to fabricate, lack mechanical robustness or are made from non-renewable, non-degradable materials.

The sponge, created by Chinese researcher, Mr Xiaoqing Wang and his team, is made by treating natural balsa wood with chemicals that removed lignin and hemicellulose, leaving behind a cellulose skeleton. The remaining highly porous structure was then coated with a hydrophobic coating that attracted oil and repelled water.

When placed in a mixture of water and silicone oil, the wood sponge removed all of the oil, leaving clean water behind. Depending on the oil tested, the sponge absorbed 16 to 41 times its own weight, which scientists say is equal to or better than most other reported absorbents.

After soaking up oil, the sponge can be simply squeezed out like a normal sponge. It is capable of enduring at least 10 cycles of absorption and squeezing. It will bio-degrade upon being discarded.

Switzerland’s Empa research group has also successfully developed a sponge made from wood waste that absorbs oil, but not water.

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