Graphene: Out of the Lab and Into the World
Why graphene hasn’t taken over the world— yet.
Graphene’s an awesome material, to say the least. It’s literally 200 times stronger than steel and lighter than paper. Its atoms are also so tightly bond, hydrogen would take about a billion years to penetrate graphene. These factors along with its highly conductive features give graphene the potential to be used in hundreds of products and several fields. So why isn’t it out in the open and being used everywhere now? What’s one obstacle that if tackled could put graphene almost everywhere? The answer to this question is graphene production.
What is Graphene?
Graphene is one of the strongest materials on Earth. It actually absorbs twice as much impact as Kevlar, which is the material commonly used for bulletproof clothing. Graphene is also considered to be one of the most conductive materials and is incredibly flexible.
Graphene is a carbon-based material, and as mentioned before, has a plethora of properties and potential applications. From solar panels to efficient DNA sequencing to wearable clothing, graphene can be used for so many things. For more info, check out my article on graphene and its properties linked below!
The sole reason for the absence of graphene in, well, almost all our products is because there isn’t an efficient and cost-friendly way to mass-produce it. Graphene is a single atom thick and has better conductivity and strength in that state rather than when it hasn’t been cut into layers yet, a.k.a. when it’s still graphite. The thing is, it’s not that the production methods just suck, it’s because of graphene having the desired quality that you can’t get with every method, and also because of Van der Waals forces.
Obstacles
Desired Traits
The thing is, different methods don’t always produce the same type of graphene. For example, chemical vapor deposition (a method we’ll get into later) is ideal for flexible graphene sheets for electronics but isn’t ideal for other graphene operations that need bulk surface area and increased permeability.
In fact, the five main factors that go into the ultimate desired form of graphene are production cost, scalability, reproducibility, processability, and the quality of the graphene. Without these factors, it’ll be difficult to efficiently produce graphene that can be used in a variety of ways.
Van der Waals Forces
These are bonds that go down to the molecular level of graphene and make the atoms bond together. Although these bonds are weak on their own, they can become very strong when several of these forces interact between two objects. These forces make separating graphene tricky when using a top-down approach.
Click here for more information on Van der Waals forces!
Now that we’ve established the key obstacles that occur with the production of graphene, we can move on to some of the more common ways graphene is produced.
The Manufacturing Methods
Micromechanical Cleavage (The Tape Method)
This method consists of tape being stuck to and peeled off of graphite. Doing so leaves behind graphene flakes on the tape. The tape can then be dissolved off, leaving behind graphene!
This was one of the first methods used to isolate graphene from graphite, and was what won Andre Geim and Kostya Novoselov a Nobel prize in physics! Sticking tape to a rock definitely doesn’t sound like a notable discovery at first glance, but doing so actually helped people discover the amazing properties of graphene such as its flexibility and strength.
Obviously, this isn’t a very efficient method of production. It would be fairly amusing to watch people sit down and peel tape off a rock all day, but it would take hours to produce just a bit of graphene, and would just be very inefficient overall.
Chemical Vapor Deposition
This method is actually a bottom-up method, so it doesn’t involve the breaking down of graphite. How it works is a substrate (usually copper) is heated up to around 1000 degrees Celsius. A gas, usually methane, is then sprayed on the substrate. After a bit of time, sheets of graphene start to form because of the carbon atoms in the methane gas.
This method of chemical vapor deposition for graphene was used as a prototype in 2010 for Samsung to make rectangular films of graphene screens for phone screens. The method isn’t the best for other forms of graphene inventions, and the graphene produced can also be low quality. Copper can be expensive to purchase, and the process itself takes time and isn’t immediate.
Oxidation of Graphite
This method isn’t for producing just graphene per se, but is for producing graphene oxide. For a brief intro, graphene oxide is an oxidized form of graphene (a combination of hydrogen, carbon, and oxygen) and is also a single atom thick. The oxidization makes the material easy to process because it’s dispersible in water and can be used to make graphene. This can’t be used for some of the things normal graphene is used for but can be used for things like the coating on substrates and in flexible electronics.
Graphene oxide is also easier to manufacture, fluorescent, and even cheaper than graphene, but that’s an article for another time.
There are different methods of making graphene oxide, but I’ll talk about the most popular method, the Hummers method. Oxidizing agents like sulfuric/nitric acid and potassium permanganate can be used to exfoliate graphene layers. Small energy input such as stirring can break the graphite into sheets of graphene, forming graphene oxide!
Different methods can have different effects on the quality and conductivity of the graphene produced. The chemicals involved in this procedure can also be very harmful and difficult to clean up, which is why the method (along with the others in the article) is actively trying to be improved.
This method is actually a form of liquid-phase exfoliation, which will be talked about below!
Liquid Phase Exfoliation (LPE)
There are different forms of LPE, but we’ll be talking about the more commonly used one using sonication. There are three key steps in this process — dispersion of graphite in a solvent, exfoliation, and purification.
- Dispersion of graphene in a solvent
This step is pretty self-explanatory; graphite is dispersed into a solvent that eventually breaks down the graphite into graphene. The solvent choice here is extremely crucial to the process, as it can determine the effectiveness of graphite exfoliation and how well the graphene sheet will be thermodynamically established. - Exfoliation
This is the stage where the graphite actually breaks into graphene. The ultrasound waves do a good job aiding the process of the breaking down of graphite and extracting individual graphene layers. - Purification
This stage is necessary to separate exfoliated flakes from unexfoliated flakes. It can be carried out with the help of centrifugation, which is essentially the spinning of graphene in a chamber at high speed. The unexfoliated flakes are separated from the exfoliated flakes, and the exfoliated flakes come together to form a graphene sheet.
This method can be very scalable because of its simplicity and the resulting graphene quality. Van der Waals is a prevalent problem here because this is a top-down approach, so a surfactant can be added to prevent the bonding of graphene layers. If the manufacturer is very specific with the kind of solvent and surfactant being used, this method is overall pretty simple and cost-effective!
Laser Ablation
Laser energy can be used in different ways to exfoliate graphite and to create graphene. For example, Professor James M. Tour’s Research Group at Rice University published a scalable approach to graphene production. The method consists of converting the surface of polymer films into graphene patterns using an infrared laser.
Another example would be using laser pulses to remove graphene directly from graphite. The key to separating the graphene, in this case, would be tuning the laser energy density required for exfoliation, increasing the density when decreasing the graphene layer count.
There are several other ways of using lasers to separate graphene from graphite, but since the methods aren’t very widely used and may not be scalable for a while, there isn’t a lot of research on the subject.
There are also newer, much more creative methods that are pretty unique!
Using a Blender
You read that right; graphene can literally be made with a blender. All you do is place graphite and dishwasher soap (or another similar solvent) in a blender, exfoliation occurs, and graphene layers separate! This method could potentially be scaled and used with larger mechanisms.
Using Soybean Oil
This method is also pretty interesting, considering it actually works. Soybean oil is heated in a furnace for about 30 minutes on top of nickel foil, and bam — out comes graphene! It is important to control the temperature in this method, as forgetting to do so could prevent the graphene from even forming.
Conclusion
As shown, graphene has several barriers and obstacles to overcome when it comes to its production. Some production methods are better than others, some need only a couple of modifications to become scalable, and some are just incredibly creative. When the right production method is found, graphene could make its way into our lives and into all our technology — from our batteries to our food packaging.
