Nanosheets Soak Up Spills
A material capable of absorbing up to 33 times its own weight in oils and organic solvents has been developed by scientists in Australia.
The clean-up of oil spills has historically been an expensive and lengthy process, and recent large-scale spillages - such as that from the Deepwater Horizon oil rig in 2010 - highlighted the urgent need for new and reliable water cleaning techniques. Freshwater supplies are also at risk of contamination with organic solvents and dyes discharged by the textile, tannery and paper industries.
But a solution may be in hand. A group from Deakin University in Australia, led by Ying Chen, have developed a porous boron nitride nanopowder, capable of rapidly soaking up over 30 times its own weight in oils, organic solvents and dyes.
To work like this, a material must have a high capacity and large surface area, it must be capable of accommodating high strains (so that it can swell up), and it should be lightweight and easy to separate from water. The material made by Chen and his team ticks all of these boxes.
Their powder consists of individual sheets of boron nitride (BN). At just 1.1 nanometres thick, they're thousands of times thinner than the average human hair. Large pores in each sheet gives the material an incredibly high surface area, allowing it to absorb large quantities of dyes. The BN nanosheets are also hydrophobic, meaning that they repel water and can float on the surface of a spill. Chen also found that when the sheets absorbed engine oil, they could swell by up to 37%, but without causing long-term damage to the structure of the sheet.
1 g of the nanosheets can absorb up to 33 g of impurities; everything from solvents like ethanol and toluene, to heavy-duty engine and pump oils. The process is also very fast; according to Chen, "After just two minutes, all oil has been taken up by the nanosheets".
BN nanosheets are also cost effective - the raw materials are inexpensive, and the production of the final flakes follows a standard industrial process, according to Weiwei Lei, another author of this study. Once the sheets are saturated by the spill, they can be easily collected, cleaned by burning, heating or washing, and recycled, ready to be used several times more.
Other efficient absorption materials for water purification exist, but these are based mostly on carbon. Currently, only these BN nanosheets offer a low- cost, high-capacity, recyclable material which is suitable for use on a wide range of pollutants. Lei is confident that they can scale up their production process, saying "I can't see much technical obstacle from large-scale application", so it shouldn't be too long before we see these nanosheets on the market.