by Richard Van Noorden  / 20 Apr 2014

Buried in the supplementary information of a research paper published today is a domestic recipe for producing large quantities of clean flakes of graphene. The carbon sheets are the world’s thinnest, strongest material;  electrically conductive and flexible; and tipped to transform everything from touchscreen displays to water treatment. Many researchers — including Jonathan Coleman at Trinity College Dublin — have been chasing ways to make large amounts of good-quality graphene flakes.

In Nature Materials, a team led by Coleman (and funded by the UK-based firm Thomas Swan) describe how they took a high-power (400-watt) kitchen blender and added half a litre of water, 10–25 millilitres of detergent and 20–50 grams of graphite powder (found in pencil leads). They turned the machine on for 10–30 minutes. The result, the team reports: a large number of micrometre-sized flakes of graphene, suspended in the water. Coleman adds, hastily, that the recipe involves a delicate balance of surfactant and graphite, which he has not yet disclosed (this barrier dissuaded me from trying it out; he is preparing a detailed kitchen recipe for later publication). And in his laboratory, centrifuges, electron microscopes and spectrometers were also used to separate out the graphene and test the outcome. In fact, the kitchen-blender recipe was added late in the study as a bit of a gimmick — the main work was done first with an industrial blender.

Still, he says, the example shows just how simple his new method is for making graphene in industrial quantities. Thomas Swan has scaled the (patented) process up into a pilot plant and, says commercial director Andy Goodwin, hopes to be making a kilogram of graphene a day by the end of this year, sold as a dried powder and as a liquid dispersion from which it may be sprayed onto other materials. “It is a significant step forward towards cheap and scalable mass production,” says Andrea Ferrari, an expert on graphene at the University of Cambridge, UK. “The material is of a quality close to the best in the literature, but with production rates apparently hundreds of times higher.”

The quality of the flakes is not as high as that of the ones the winners of the 2010 Nobel Prize in Chemistry, Andre Geim and Kostya Novoselov from Manchester University, famously isolated using Scotch Tape to peel off single sheets from graphite. Nor are they as large as the metre-scale graphene sheets that firms today grow atom by atom from a vapour. But outside of high-end electronics applications, smaller flakes suffice — the real question is how to make lots of them. Although hundreds of tons of graphene are already being produced each year — and you can easily buy some online — their quality is variable. Many of the flakes in store are full of defects or smothered with chemicals, affecting their conductivity and other properties, and are tens or hundreds of layers thick. “Most of the companies are selling stuff that I wouldn’t even call graphene,” says Coleman.

After experimenting with the kitchen blender, the team used the more professional rotor-stator device which combines rotating blades and a stationary screen to filter the graphene flakes (Photo: CRANN)

The blender technique produces small flakes some four or five layers thick on average, but apparently without defects — meaning high electrical conductivity. Coleman thinks the blender induces shear forces in the liquid sufficient to prise off sheets of carbon atoms from the graphite chunks (“as if sliding cards from a deck”, he explains). Kitchen blenders aren’t the only way to produce reasonably high-quality flakes of graphene. Ferrari still thinks that using ultrasound to rip graphite apart could give better materials in some cases. And Xinliang Feng, from the Max Planck Institute for Polymer Research in Mainz, Germany, says that his recent publication, in the Journal of the American Chemical Society, reports a way to produce higher-quality, fewer-layer graphene at higher rates by electrochemical means. (Coleman points out that Thomas Swan have taken the technique far beyond what is reported in the paper.)

As for applications, “the graphene market isn’t one size fits all”, says Coleman, but the researchers report testing it as the electrode materials in solar cells and batteries. He suggests that the flakes could also be added as a filler into plastic drinks bottles — where their added strength reduces the amount of plastic needed, and their ability to block the passage of gas molecules such as oxygen and carbon dioxide maintains the drink’s shelf life. In another application altogether, a small amount added to rubber produces a band whose conductivity changes as it stretches — in other words, a sensitive strain sensor. Thomas Swan’s commercial manager, Andy Goodwin, mentions flexible, low-cost electronic displays; graphene flakes have also been suggested for use in desalination plants and even condoms. In each case, it has yet to be proven that the carbon flakes really outperform other options — but the new discoveries for mass-scale production mean that we should soon find out. At the moment, an array of firms is competing for different market niches, but Coleman predicts a thinning-out as a few production techniques dominate. “There are many companies making and selling graphene now: there will be many fewer in five years’ time.”

Bottles filled with water, detergent and graphene flakes – the graphene absorbs a small amount of light, leading to the darkened appearance of the mixture (Photo: CRANN)

Make graphene in your kitchen with soap and a blender
by Jacob Aron / 20 April 2014

First, pour some graphite powder into a blender. Add water and dishwashing liquid, and mix at high speed. Congratulations, you just made the wonder material graphene. 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.

Carbon smoothie
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.

Useful defects
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 MaterialsDOI: 10.1038/nmat3944}

A piece of silicon carbide disk is covered with a layer of graphene (2012). {REUTERS/Kacper Pempel}

Graphene supercapacitors are 20 times as powerful, can be made with a DVD burner
by  on March 19, 2012

A team of international researchers have created graphene supercapacitors using a LightScribe DVD burner. These capacitors are both highly flexible (pictured below) and have energy and power densities far beyond existing electrochemical capacitors, possibly within reach of conventional lithium-ion and nickel metal hydride batteries. The team, which was led by Richard Kaner of UCLA, started by smearing graphite oxide — a cheap and very easily produced material — films on blank DVDs. These discs are then placed in a LightScribe drive (a consumer-oriented piece of gear that costs less than $50), where a 780nm infrared laser reduces the graphite oxide to pure graphene. The laser-scribed graphene (LSG) is peeled off and placed on a flexible substrate, and then cut into slices to become the electrodes. Two electrodes are sandwiched together with a layer of electrolyte in the middle — and voila, a high-density electrochemical capacitor, orsupercapacitor as they’re more popularly known.

Energy/power density of graphene (LSG) capacitors

Now, beyond the novel manufacturing process — the scientists are confident it can be scaled for commercial applications, incidentally — the main thing about LSG capacitors is that they have very desirable energy and power characteristics. Power-wise, LSG supercapacitors are capable of discharging at 20 watts per cm3, some 20 times higher than standard activated carbon capacitors, and three orders of magnitude higher than lithium-ion batteries. Energy-wise, we’re talking about 1.36 milliwatt-hours per cm3, about twice the density of activated carbon, and comparable to a high-power lithium-ion battery.

Flexible graphene capacitor

These characteristics stem from the fact thatgraphene is the most conductive material known to man — the LSG produced by the scientists showed a conductivity of 1738 siemens per meter (yes, that’s a real unit), compared to just 100 siemens for activated carbon. The performance of capacitors is almost entirely reliant on the surface area of the electrodes, so it’s massively helpful that one gram of LSG has a surface area of 1520 square meters (a third of an acre). As previously mentioned, LSG capacitors are highly flexible, too, with no effect on its performance. These graphene supercapacitors could really change the technology landscape. While computing power roughly doubles every 18 months, battery technology is almost at a standstill. Supercapacitors, which suffer virtually zero degradation over 10,000 cycles or more, have been cited as a possible replacement for low-energy devices, such as smartphones. With their huge power density, supercapacitors could also revolutionizeelectric vehicles, where huge lithium-ion batteries really struggle to strike a balance between mileage, acceleration, and longevity. It’s also worth noting, however, that lithium-ion batteries themselves have had their capacity increased by 10 times thanks to the addition of graphene. Either way, then, graphene seems like it will play a major role in the future of electronics. {Science}

The bottom corner of a piece of graphene penetrates a cell membrane - mechanical propertie...

Wonder-material graphene could be dangerous to humans and the environment
by  / April 30, 2014

I’ve been waiting for some time now to write a headline along the lines of “scientists discover thing that graphene is not amazing at” … and here it is. Everybody’s favorite nanomaterial may have a plethora of near-magical properties, but as it turns out, it could also be bad for the environment – and bad for you, too. It’s easy to get carried away when you start talking about graphene. Comprised of single atom thick layers of carbon, graphene is incredibly light, incredibly strong, extremely flexible and highly conductive both of heat and electricity. Its properties hold the promise of outright technological revolution in so many fields that it has been called a wonder material. But it’s only been 10 years since graphene was first isolated in the laboratory, and as researchers and industries scramble to bring graphene out of the lab and into a vast range of commercial applications, far less money is being spent examining its potential negative effects.

Two recent studies give us a less than rosy angle. In the first, a team of biologists, engineers and material scientists at Brown University examined graphene’s potential toxicity in human cells. They found that the jagged edges of graphene nanoparticles, super sharp and super strong, easily pierced through cell membranes in human lung, skin and immune cells, suggesting the potential to do serious damage in humans and other animals. “These materials can be inhaled unintentionally, or they may be intentionally injected or implanted as components of new biomedical technologies,” said Robert Hurt, professor of engineering and one of the study’s authors. “So we want to understand how they interact with cells once inside the body.”

Another study by a team from University of California, Riverside’s Bourns College of Engineering examined how graphene oxide nanoparticles might interact with the environment if they found their way into surface or ground water sources. The team found that in groundwater sources, where there’s little organic material and the water has a higher degree of hardness, graphene oxide nanoparticles tended to become less stable and would eventually settle out or be removed in sub-surface environments. But in surface water such as lakes or rivers, where there’s more organic material and less hardness, the particles stayed much more stable and showed a tendency to travel further, particularly under the surface. So a spill of these kinds of nanoparticles would appear to have the potential to cause harm to organic matter, plants, fish, animals, and humans. The affected area could be quick to spread, and could take some time to become safe again. “The situation today is similar to where we were with chemicals and pharmaceuticals 30 years ago,” said the paper’s co-author Jacob D. Lanphere. “We just don’t know much about what happens when these engineered nanomaterials get into the ground or water. So we have to be proactive so we have the data available to promote sustainable applications of this technology in the future.”

At this stage, the Material Safety Data Sheet governing the industrial use of graphene is incomplete. It’s listed as a potential irritant of skin and eyes, and potentially hazardous to breathe in or ingest. No information is available on whether it has carcinogenic effects or potential developmental toxicity. But researchers from the first study point out that this is a material in its infancy, and as a man-made material, there are opportunities at this early stage to examine and understand the potential harmful properties of graphene and try to engineer them out. We’ve got a few years yet before graphene really starts being a big presence in our lives, so the challenge is set to work out how to make it as safe as possible for ourselves and our planet.

The Brown University research was published online in the Proceedings of the National Academy of Sciences. The UC Riverside paper was published in a special issue of the journal Environmental Engineering Science. {Sources: Brown UniversityUC Riverside}

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