Mass-producing graphene: An easy solution

High-quality graphene sheets are produced in a simple and rapid way using easily soluble expanded graphite.

The excellent properties of graphene potentially offer many industrial applications. However, one of the major challenges is the mass production of these carbon sheets by fast and reliable methods.

A promising strategy is based on the dispersion of expanded graphite, where graphite is first intercalated with specific molecules. With increasing temperature, the vapor pressure of the intercalating substance increases and expands the graphite, which can then be easily dispersed in solution. However, this method is complex and time consuming, and usually yields films composed of large numbers of graphene layers, instead of the desired single-layered graphene.

Fig. 1: Scanning electron microscope image of easily soluble expanded graphite.

Ji-Beom Yoo and colleagues¹ now demonstrate a new single-step method for synthesizing graphene, again based on expanded graphite, but yielding much better results. Using a simpler and more rapid approach, the team produced easily soluble expanded graphite from a fluorinated graphite intercalation compound synthesized by mixing pure graphite with the intercalating agent ClF₃. The thermal expansion in this case occurs not only because of the increasing vapor pressure of the intercalating material, but also due to the formation of gaseous fluorocarbons (primarily CF₄).

The efficiency of the expansion was clearly visible by transmission electron microscopy, which showed a distance between the graphene layers ranging between 3.64 Å and 3.94 Å, considerably larger than that (3.38 Å) for graphite expanded by other methods and ordinary graphite (3.35 Å). This result was confirmed by Raman spectroscopy, which showed a distinct electronic decoupling of the layers.

To obtain graphene suspensions, the researchers dispersed their easily soluble expanded graphite in solution and observed that at least 90% of the resulting films were less than five layers thick. The suspensions were then used to obtain transparent conducting films, which showed relatively low resistance (~3 KΩ/square) and high transparency (~80%).

These very encouraging results show that this one-step exfoliation method could be used to produce large amounts of high-quality graphene films for device applications.