The Role of Graphene in Chemistry

Core Concepts

In this article, you will learn the key differences between graphene and graphite, and how graphene’s physical and chemical properties lend itself well to various applications.

Introduction

Graphene is a thin layer of tightly packed carbon atoms, arranged in a honeycomb pattern. The name “graphene” was first brought up in 1987 to describe a single sheet of graphite. Graphene is a fundamental building block of graphitic materials.

To be clear, graphene and graphite, despite their similar names, are very different materials. Graphite is made up of graphene. However, they are physically differentiated by the amount of their layers. There is still debate on the concrete number, but it is generally accepted that 30 layers and fewer are described as multilayer graphene, while over 30 layers refers to graphite. Graphite, often used in pencils, is quite malleable and naturally occurring in sedimentary rocks. Meanwhile, graphene has a plethora of commercial applications in supercapacitors, solar cells, water filtration, and even paint!

How and when was graphene discovered?

Graphene was technically not discovered! Credit is given to Hanns-Peter Boehm for formally defining the term graphene. However, the first proper isolation and characterization of graphene was performed by Andre Geim and Konstantin Novoselov in 2004. This incredibly unique material sparked the imagination of scientists across fields to the possibilities.

They achieved this “discovery” through a process called micromechanical cleavage, a mechanical exfoliation technique referring to separating the bonds between layers of graphite. Micromechanical cleavage can be done in a variety of different ways. One simple way is with common household Scotch tape, using its adhesive backing to apply force directly and separate off a single layer of graphene. This was the original method used to produce graphene, and is still used today in industry! However, it is very time-consuming, so another method is using sound waves to agitate the particles, known as sonification. Currently, research is being done in hopes of further improving the cleavage process, making it more seamless and less reliant on tape.

Chemical Properties of Graphene

With a chemical formula of C, graphene is one of the most interesting carbon allotropes! Graphene is made up of sp²hybridized carbons, forming extremely strong covalent bonds. The London dispersion forces causing induced dipoles within the molecule also help in stabilizing the molecule.

Graphene is a relatively inert material, not eagerly interacting with other atoms due to its high stability. It is extremely conductive, allowing electrons to easily pass through. A result of the extremely small band gap, graphene is called a zero-gap semiconductor. Zero-gap refers to the small distance between the valence band and conduction band. Additional layers of graphene lead to s-p orbital mixing within the molecule, which increases the energy required for electrons to “jump” up. This represents a reduction in electron mobility (the speed at which the electron can move up bands). As the thickness of graphene increases, so does the band gap, requiring more energy and time for electrons to move.

Physical Properties of Graphene

Graphene is considered the thinnest allotrope known today, with a thickness of approximately 0.34 nanometers, which is the thickness of one carbon atom! Graphene is also praised for its strength, estimated to be about 100 or more times stronger than steel. This strength is due to its chemical composition that we discussed above. Graphene’s strong covalent bonding, combined with the influence of London dispersion forces, make for extremely stable bonds! All in all, its unique physical properties make it an impressive material.

Applications

Graphene is a technological powerhouse, popularly used in chemical, biological and magnetic sensors, preventative coatings, and even energy storage. Graphene research has been thriving in terms of supercapacitors and batteries. Its incredible electrical conductivity, coupled with its flexibility, makes graphene an excellent material for wearable technology. The thinness of graphene is why it is so flexible, as the bonds themselves don’t actually have much flexibility.

Graphene’s thermal sensitivities when doped also make it ideal for in-field equipment operating, more efficiently than the common silicon. Doping is the process of introducing a new substance in a semiconductor; in this case, scientists have been exploring the applications of introducing copper to graphene.

Similarly, graphene has been shown to improve efficiency in solar cells by increasing the number of active sites on the cell. The solar cells benefit from its high conductivity, small band gap and inert nature! However, scientists are working to make graphene better at holding charge, and are exploring the use of graphene oxide. Also taking advantage of its inert nature, the application of graphene in corrosion-resistant paint is currently being explored for use on cars and ships.

Conclusion

In this article we discussed graphene, a carbon allotrope hailed by chemists, engineers, and physicists as an incredible material. We learned what separates graphene from graphite, and why they have such different properties. We expounded on how graphene’s chemical makeup explains its physical properties, and how scientists can apply these properties in the real world. From magnetic sensors to corrosion-resistant paint, graphene is a versatile player in the materials science world!