One of the most exciting developments in carbon chemistry over the last five years has been the explosion of research into graphene. Graphene is an extremely thin (one atom thick) sheet of carbon atoms that are in the shape of hexagons, each sharing common sides to form a flat hexagonal grid. Graphene has some pretty miraculous electronic properties as a result of the overlap of molecular orbitals within the structure. It’s being investigated for use in electrical components, as a replacement for silicon in transistors and other circuitry, and for all manner of molecular electronics that are based on lightweight, durable carbon materials. However, graphene has a significant drawback: it’s devilishly hard to make.
Graphene exists in Nature in the form of graphite. Graphite is a slippery powder often used as a lubricant for padlocks and for automobile applications; it’s also used in applications which require a high resistance to heat, such as crucibles and rocket engine exhausts. On the molecular scale, graphite consists of trillions of individual graphene sheets, all stacked up into a clumsy pile. The sheets each individually have a lot of structural integrity, but they can slip and slide past each other extremely easily due to a lack of significant intermolecular interactions; the graphene does not possess a permanent dipole, and also can’t interact in any type of hydrogen bonding. So the pile of sheets acts as a fantastic lubricant, as each of the graphene molecules slips right past all of the other sheets in the pile.
As you might imagine, trying to somehow lift a single, individual sheet from the pile of graphite is not an easy task. The sheets are as thin as they can possibly be – only one atom thick. They’re stuck in the middle of a slick, slippery pile. We really don’t even have the technology to address something that thin, let alone manipulate it away from a lubricated mass. About the only way that scientists have been able to do this “graphene from graphite” procedure has been to take a piece of sticky tape and to “peel” away flakes from the graphite, passing it back and forth between fresh pieces of tape until finally there is only one single molecule left on the surface of the tape. The adhesive tape is then burnt away, leaving the graphene molecule behind. However, this type of synthesis – which by definition, generates the graphene one molecule at a time – is ludicrously slow and is a completely inefficient use of the researchers time. If graphene is ever going to become more than a laboratory curiousity and be used in a commercial application, scientists need a large-scale method of generating a lot of graphene at once. However, we can’t afford to synthesize the graphene in a flask or a pot – the sheets would just pile up and we’d be right back to where we started, with a pile of graphite.
I was therefore excited to read an article in the journal Nature: Chemistry that discussed a new method of graphene synthesis that relied on organic synthesis. It was so simple. That’s often the hallmark of true innovation. Researchers took a material related to graphite – graphite oxide, which is sheets of graphite that also have oxygen atoms attached – and made a slurry in water. They then took a glass microscope slide and spun it rapidly on a table top; the water-graphite oxide slurry was then dropped onto the surface of the moving glass using an eyedropper. The centrifugal force of the slides motion “slung” the water droplets off of the surface at a high speed. As a result, the graphite oxide was coated across the glass surface in an extremely thin (one atom thin) layer. After the slide had dried, the researchers exposed the slide to a number of chemical treatments, including borohydride and concentrated sulfuric acid. These treatment steps reduced the oxidized groups on the graphite and removed the oxygen atoms. What was left over was the molecular sheet of graphene, which could then be lifted off of the glass relatively easily as it wasn’t part of a slippery bulk material. Because the method of slide coating (which is called spin-coating) can be scaled up very easily, it’s now very easy to make a lot of graphene at once without fiddling around with Scotch tape.
Now that researchers have a method of producing a large amount of graphene, they finally have sufficient starting material for all of the experiments that they want to perform, and they also have a source of material to use in a commercial product. This is a very solid breakthrough in the area of graphene chemistry.
Source for this article can be found at: http://www.nature.com/nchem/journal/v1/n5/full/nchem.281.html