This surprisingly simple recipe is now the easiest way to mass-produce pure graphene – sheets of carbon just one atom thick. The material has been predicted to revolutionise the electronics industry, based on its unusual electrical and thermal properties. But until now, manufacturing high-quality graphene in large quantities has proved difficult – the best lab techniques manage less than half a gram per hour.
“There are companies producing graphene at much higher rates, but the quality is not exceptional,” says Jonathan Coleman of Trinity College Dublin in Ireland.
Coleman’s team was contracted by Thomas Swan, a chemicals firm based in Consett, UK, to come up with something better. From previous work they knew that it is possible to shear graphene from graphite, the form of carbon found in pencil lead. Graphite is essentially made from sheets of graphene stacked together like a deck of cards, and sliding it in the right way can separate the layers.
The team put graphite powder and a solvent fluid in a laboratory mixer and set it spinning. Analysis with an electron microscope confirmed that they had produced graphene at a rate of about 5 grams per hour. To find out how well the process could scale, they tried out different types of motors and solvents. They discovered that a kitchen blender and Fairy Liquid, a UK brand of dishwashing liquid, would also do the job.
“If you are using a blender, why use a fancy expensive surfactant? Why not use the simplest surfactant there is, and I guess that is Fairy Liquid,” says Coleman.
Still, Coleman says you may not want to try this at home. The exact amount of dishwashing liquid required depends on the properties of the graphite powder, such as the size distribution of the grains and whether any materials other than carbon are contaminating the sample. These can only be determined using advanced lab equipment. The method also doesn’t convert all the graphite to graphene, so the two materials have to be separated afterwards.
“It is a fun experiment, but it wouldn’t get you very far,” says Colman. “You could make black liquid full of graphene, but what’s the next step?” Instead, the team’s calculations suggest the technique is scalable to industrial levels – a 10,000 litre vat with the right motor could produce 100 grams per hour. Thomas Swan has already started work on a pilot system.
Coleman is excited about the scientific potential of cheap, abundant graphene. For example, a previous lab experiment showed that adding a dash of graphene to a type of polyester boosted its strength by 50 per cent, since graphene is one of the strongest known materials. The new production method would yield enough graphene to scale this up for industrial processes, which normally involve kilograms of raw material.
Andrea Ferrari at the University of Cambridge says the ability to produce large quantities of high-quality graphene is useful, but not essential for all applications. Graphene with defects binds more easily to other molecules, making it suitable for developing batteries or composite materials.
Still, the simplicity of the method echoes the original isolation of graphene by Andre Geim and Konstantin Novoselov at the University of Manchester. They used sticky tape and a pencil, a method that won them a Nobel Prize in 2010.
“Our initial plans for scale up were in hindsight terribly complicated, which turned out to be unnecessary,” says Coleman. “Perhaps we are bad at realising how simple things can be.”
Journal reference: Nature Materials, DOI: 10.1038/nmat3944
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