Graphene? Graphene nanoplatelet? Graphite oxide? Graphene oxide? Reduced graphene oxide? To see how to describe the unified definition of graphene in 1 min
The controversy on the definition of graphene
Graphene is a single layered nanomaterial with a similar two-dimensioned structure characteristic to traditional graphite. The two-dimensioned structure consists of a continuous honeycomb rings connected by carbon atoms in sp2 bonding. With this similar structure to traditional graphite structure, it is easy to have a confusion in definition with both the early development of thin-layer graphite or expanded graphite.
How to define the graphene?
Back in the editor meeting to journal of Carbon held at Jiju Island, Korea in 2014, Professor Robert Hurt, the chief editor of journal of Carbon, had come up with a much clear theory on the structure definition in order to unify the current disagreement about graphene. Professor Hurt proposed a literally definition as a standard based on how many layers of graphene. The single layered graphene, graphene, is a 2-D sheet-like structure consist of a continuous honeycomb rings；bi-layered graphene and tri-layered graphene consist of two or three layers of graphene, and it could exist in a powder form or film; few-layered graphene refer to the structure are stacking with 2-5 layers of graphene； finally, the graphite nanoplatelet, graphite sheet, thin-layered graphene, graphite nanoflake, it refer to a two-dimensional thin layered graphite in which the thickness is less than 100 nm and the structure type is not limited to the 2H or the 3C structure.
What is the graphite oxide, graphene oxide or reduced graphene oxide ?
Graphite oxide and graphene oxide are named because of the contained oxygen functional group, the major difference comes from the thickness and layers. Typically, graphene oxide is the product after a exfoliation process of graphite oxide. The oxygen contained group comes from graphite structure strong oxidized by the acid during the reaction. These oxygen-contained groups could be easily removed by proper reduction process, the products after reduction process could be called as reduced graphene oxide. Final residual content of oxygen-contained group will be usually determined by what reduction process or the conditions we use. Using a proper reduction process will not only remove the oxygen-contained group from the products, but also could recovery the crystal structures damaged by the strong oxidized reaction.
Summary
In a short words, it could be used a simple way to define the graphene, thin layered graphene, graphite oxide, graphene oxide, or reduced graphene oxide by the number of layers and the index of residual oxygen amount. Graphene could be defined as a 2-D sheet-like structure with a layer numbers below 10 or a thickness below 5nm. The characteristic of oxygen contained groups could distinguish two catalogs of graphene (without oxygen) and graphene oxide (with oxygen), these two different structure could refer to conduction an mechanical enhancement applications. Therefore, the option for graphene could be determined by the end-application, for example, the thermal or electrical conduction applications could choose the graphene with lower oxygen contain and higher crystallinity. In the other hand, the mechanical reinforcement application enhanced by graphene could use the graphene oxide or reduced graphene oxide as additive.