Covalent graphene

The covalent methods previously discussed for fullerene modification using cycloaddition reactions also can be applied to carbon nanotubes. This strategy results in chemically linking molecules to the graphene rings on the outer surface of the cylinder, resulting in stable... 

Although there have been great advances in covalent functionalization of fullerenes to obtain surface-modified fullerene derivatives or fullerene polymers, the application of these compounds in composites still remains unexplored, basically because of the low availability of these compounds [132]. However, until now, modified fullerene derivatives have been used to prepare composites with different polymers, including acrylic [133,134] or vinyl polymers [135], polystyrene [136], polyethylene [137], and polyimide [138,139], amongst others. These composite materials have found applications especially in the field of optoelectronics [140] in which the most important applications of the fullerene-polymer composites have been in the field of photovoltaic and optical-limiting materials [141]. The methods to covalently functionalize fullerenes and their application for composites or hybrid materials are very well established and they have set the foundations that later were applied to the covalent functionalization of other carbon nanostructures including CNTs and graphene. 

M. Fang, K. G. Wang, H. B. Lu, Y. L. Yang, S. Nutt, Covalent polymer functionalization of graphene nanosheets and mechanical properties of composites, Journal of Materials Chemestry, vol. 19, pp. 7098-7105, 2009. 

H. F. Yang, C. S. Shan, F.H. Li, D.X. Han, Q. X. Zhang, L. Niu, Covalent functionalization of polydisperse chemically-converted graphene sheets with amine-terminated ionic liquid, Chemical Communications, vol. 26, pp. 3880-3882, 2009. 

E. Spiecker, F. Hauke, A. Hirsch, Covalent bullk functionalization of graphene, Nature Chemestry, vol. 3, pp. 279-286, 2011. 

A. Ghosh, K.V. Rao, R. Voggu, S. J. George, Non-covalent functionalization, solubilization of graphene and single-walled carbon nanotubes with aromatic donor and acceptor molecules, Chemical Physics Letters, vol. 488, pp. 198-201, 2010. 

The majority of studies have used surfactants that wrap around nanocarbons via van der Waals interactions [37]. For instance, surfactants such as sodium dodecylsulfate (SDS) are commonly used to disperse CNTs in aqueous solutions [38,39] while other surfactants, such as Pluorinc-123, are used to mechanically exfoliate graphene from graphite flakes (Fig. 5.4(a)) [40,41]. The polar head group of the surfactant can be used to further hybridize the nanocarbon via a range of covalent or noncovalent interactions [42]. For example, nanoparticles of Pt [43,44] and Pd [45] have been decorated onto SDS-wrapped MWCNTs. Similarly, Whitsitt et al. evaluated various surfactants for their ability to facilitate the deposition of Si02 NPs onto SWCNTs [46,47]. As an exam-... 

Yang, C., et al., Conjugates of graphene oxide covalently linked ligands and gold nanoparticles to construct silver ion graphene paste electrode. Talanta, 2012. 97(0) p. 406-413. 

Hu, H., et al., Microwave-assisted covalent modification of graphene nanosheets with chitosan and its etectrorheological characteristics. Applied Surface Science, 2011. 257(7) p. 2637-2642. 

Xu, Y., et al., A graphene hybrid material covalently functionalized with porphyrin Synthesis and optical limiting property. Advanced Materials, 2009. 21(12) p. 1275-1279. 

It often becomes necessary to prepare dispersions of graphene in organic or aqueous media [73-74]. For this purpose, different approaches have been successfully employed for few-layer graphene. The two main approaches for obtaining this type of graphene are covalent functionalization or by means of noncovalent interactions. There has been some recent effort to carry out covalent and noncovalent functionalization of graphene with aromatic molecules, which help to exfoliate and stabilize the individual graphene sheets and to modify their electronic properties [75 84]. 

Fig. 4.8 Structure of graphite, pointing to 3D hexagonal unit and covalent bonds between carbon atoms, and van der Walls bonds between graphene planes and hydrogen...

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