Graphene Modification

As a molecular sheet of graphite, graphene is comprised of a single layer of carbon atoms set in a hexagonal lattice. It is the simplest structural element of different allotropes of carbon (graphite, carbon nanotubes, etc.) and it can be deliberated as an indeterminately huge aromatic molecule. Since its first isolation from graphite by two researchers at The University of Manchester, Prof. Andre Geim and Prof. Kostya Novoselov in 2004, graphene has undoubtedly emerged as one of the most promising nanomaterials because of its unique combination of superb mechanical, electrical and thermal properties. For example, graphene is the toughest material ever found and is nearly transparent. It also provides proficient heat and electrical conductivity. Graphene demonstrates a large and nonlinear diamagnetism, which is more than that of graphite, and can be ascended by neodymium magnets. Because of these extraordinary properties a great deal of interest is generated on the graphene research, including theoretical and experimental studies. Those studies open a way for graphene’s exploitation in a wide spectrum of applications ranging from electronics to optics, sensors, biodevices and energy-storage devices.

Covalent functionalization of the epoxy groups of graphene oxide by an ionic liquid. Reprinted from Ref 1.*

As mentioned above, graphene finds a great amount of applications during the past decade. However, its insolubility in most organic and inorganic solvents adversely impacts the potential for solution-phase processing. Chemical modification of graphene through covalent or non-covalent interactions to obtain new graphene derivatives has attracted a lot of interest. Graphene oxide (GO), derived from the oxidation of graphite, possesses abundant reactive oxygen functional groups, which not only render GO moderate water-dispersibility but also offer reactive sites for the further modification. For example, people have modified GO with long-chain alkylamine to make it dispersed well in organic solvent. Porphyrin and fullerene modified-graphene has been proven to afford the useful nonlinear optical properties. Besides small molecules, polymer modified GO has also been studied in several research works. In polymer composite applications, the solubility of graphene sheets should be maximized in a common solvent with that of the matrix polymer and the stress transfer should also be maximized through the interface due to the specific interaction between the sheet and polymer matrix. Current approaches for preparing covalent bonded polymer on graphene surface include the ‘grafting to’ approach, involving radical coupling or reaction with edge-bound carboxylic acid groups on GO as well as the ‘grafting from’ approach, which uses initiator-functionalized graphene for polymerization.

PEG functionalized nanographene oxide for cancer drug (SN-38) delivery. Reprinted from Ref 2.*

Since various chemical modification reactions utilizing these oxygen-containing groups have been developed, doping is increasingly used as one of the most feasible methods to control the semiconducting properties of graphene. Herein, substantial effort has been made in both academia and industry, resulting in the recent burst of technologies in graphene doping, which is roughly divided into three categories: first, the hetero atom doping, including arc discharge, chemical vapor deposition, electrothermal reaction and ion-irradiation approaches; second, the chemical modification; third, the electrostatic field tuning. At Matexcel, our experts in graphene chemistry offer different strategies for graphene modification, including chemical modification, polymer grafting, and doping.

References:
1. Daniel R. Dreyer. “The chemistry of graphene oxide.” Chem. Soc. Rev. 2010.
2. Layek, Rama K. "A review on synthesis and properties of polymer functionalized graphene." Polymer 2013.

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