Graphene sheets functionalized

Fig. 32. Reversible capacity of microporous carbon prepared from phenolic resins heated between 940 to 1 I00°C plotted as a function of the X-ray ratio R. R is a parameter which is empirically correlated to the fraction of single-layer graphene sheets in the samples.

Fig. 5. Band gap as a function of nanotube radius calculated using empirical tight-binding Hamiltonian. Solid line gives estimate using Taylor expansion of graphene sheet results in eqn. (7).

The optimised interlayer distance of a concentric bilayered CNT by density-functional theory treatment was calculated to be 3.39 A [23] compared with the experimental value of 3.4 A [24]. Modification of the electronic structure (especially metallic state) due to the inner tube has been examined for two kinds of models of concentric bilayered CNT, (5, 5)-(10, 10) and (9, 0)-(18, 0), in the framework of the Huckel-type treatment [25]. The stacked layer patterns considered are illustrated in Fig. 8. It has been predicted that metallic property would not change within this stacking mode due to symmetry reason, which is almost similar to the case in the interlayer interaction of two graphene sheets [26]. Moreover, in the three-dimensional graphite, the interlayer distance of which is 3.35 A [27], there is only a slight overlapping (0.03-0.04 eV) of the HO and the LU bands at the Fermi level of a sheet of graphite plane [28,29],... 

An important route to solubilization of carbon nanotubes is to functionalize their surface to form groups that are more soluble in the desired solvent environment. It has been shown that acid treatment of nanotube bundles, particularly with HC1 or HNO3 at elevated temperatures, opens up the aggregate structure, reduces nanotube length, and facilitates dispersion (An et al., 2004 Kordas et al., 2006). Nitric acid treatment oxidizes the nanotubes at the defect sites of the outer graphene sheet, especially at the open ends (Hirsch, 2002 Alvaro et al., 2004), and creates carbonyl, carboxyl, and hydroxyl groups, which aid in their solubility in polar solvents. 

T. Ramanathan, A.A. Abdala, S. Stankovich, D.A. Dikin, M. Herrera-Alonso, R.D. Piner, et al., Functionalized graphene sheets for polymer nanocomposites, Nature Nanotechnology, 3 (2008) 327-331. 

J.R. Lomeda, C.D. Doyie, D. V Kosynkin, W.-F. Hwang, J.M. Tour, Diazonium functionalization of surfactant-wrapped chemically converted graphene sheets, Journal of the American Chemical Society, 130 (2008) 16201-16206. 

H.C. Schniepp, J.-L. Li, M.J. McAllister, H. Sai, M. Herrera-Alonso, D.H. Adamson, et al., Functionalized single graphene sheets derived from splitting graphite oxide, The Journal of Physical Chemistry, B. 110 (2006) 8535-8539. 

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. 

D. Chen, H. Zhu, T. Liu, In situ thermal preparation of polyimide nanocomposite films containing functionalized graphene sheets, ACSAppIMater Interfaces, vol. 2, pp. 3702-3708, 2010. 

Fig. 6.6 (a) A comparison of mechanical and thermal properties of PMMA hybrids with SWNT, expanded graphite (EGr) and functionalized graphene sheets (FGS). (b) Percentage synergy in hardness and modulus of the hybrids with binary nanocarbon fillers (from [44]). 

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]. 

Schniepp HC, Li JL,McAllister MJ, Sai H, Herrera-Alonso M, Adamson DH, Prud homme RK, Car R, Saviile DA, Aksay IA. Functionalized single graphene sheets derived from splitting graphite oxide, . Phys. Chem. B 2006,110, 8535-8539. 

Figure 3.2 Nearest-neighbor tight-binding calculation of the density of electronic states (DOS) as a function of energy for a graphene sheet (black), a metallic (9,0) SWNT (blue), and a semiconducting (10,0) SWNT (red).

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