Graphene continues to attract attention because of its high charge carrier mobility and robust mechanical properties, which make it desirable for application in nanoelectronics, sensors and batteries. However, in order to realize this broad range of applications, a reliable, large-scale method of producing high-quality graphene is required.

Now, Guangtao Li from Tsinghua University and colleagues1 report a self-assembly method for preparing gram quantities of single-layer graphene. They have found a way to produce graphene under mild conditions without hazardous agents, yielding sheets of up to micrometers in size.

Fig. 1: Schematic illustration of the confined self-assembly procedure for fabricating pure single-layer graphene.

Li and his colleagues used molecules that self-assemble into layered sheets. The main structure-directing component was a surfactant molecule with a pyrrole at one end — a ring of four carbons and a nitrogen atom providing a source of carbon for the graphene sheets. A lysine moiety at the other end of the surfactant chain was linked to the silicon atom in tetraethoxysilane (TEOS) during the reaction.

Mixing TEOS and sodium hydroxide with the surfactant caused the surfactant chains to assemble into stacked layers, with the layers of pyrrole rings alternating with those of TEOS. The TEOS reacted with the sodium hydroxide, yielding sheets of mesoporous silica. The researchers polymerized the pyrrole rings under mild conditions, producing two-dimensional polypyrrole sheets confined by silica on either side.

A further carbonization step then created single layers of graphene of up to several hundred nanometers in width and length. The sheets were 0.57 nm thick — very close to the 0.6 nm thickness of graphene sheets made by exfoliation. The theoretical thickness of a single graphene sheet is 0.34 nm, indicating that some impurities and defects were present.

“The crucial point of this strategy is the utilization of a confined space for producing single-layer graphene,” says Li. “Therefore, we can fabricate clean and pure single-layer graphene, which is inaccessible by the previously reported methods, under mild preparation conditions and without hazardous chemicals.”