Single-wall CNTs structure

In this chapter the results of detailed research on the realistic electronic structure of single-walled CNT (SWCNT) are summarised with explicit consideration of carbon-carbon bond-alternation patterns accompanied by the metal-insulator transition inherent in low-dimensional materials including CNT. Moreover, recent selective topics of electronic structures of CNT are also described. Throughout this chapter the terminology "CNT stands for SWCNT unless specially noted. 

CNTs have a different porous structure than activated carbon. The specific surface area of CNTs can range from 50 m2/g (multi-walled CNTs with 50 graphene walls) to 1315 m2/g (single-walled CNTs). Theoretically, the porous structure of CNTs is identical to the tubular structure of CNTs and the pore sizes of CNTs correspond to the inner diameters of opened CNTs and should have a narrow distribution. Activated carbons usually have a broad pore distribution covering micropore, meso-pore and macropore ... 

One way to define the structure of single-walled CNT is to think of each CNT as a result of rolling a graphene sheet specifying the direction of rolling and the circumference cross-section (Figure la). The unit vectors of the planar... 

A multi-walled CNT is a coaxial assembly of single-walled CNTs, normally encased by 10 to 30 consecutive layers of carbon atoms. Multi-walled CNTs are more synthesized than single-walled CNTs. In most cases multi-walled CNT contain many structural defects. Recently the synthesis of double-walled CNTs has been reported7 (Figure lc). 

Nanostructure determination is a challenge in materials characterization. Many inorganic nanostructures lack the uniformity and synunetry of a single crystal or the monodispersity of some organic molecules. Their structure determination thus requires a high-resolution probe that can examine individual nanostructures. Electron diffiaction has the resolution required the nanoprobes used in CBED and NED are especially suited for smdying nanomaterials. For structures like single-wall CNT, the structure can be determined directly from electron diffraction patterns. 

Another plausible strategy consists of the functionalization of CNTs via covalent attachment of selected groups. This is the case of thiol and thiol-plus macrocyclic ///-crown-/ ether ( = 12, n = 4, and zn = 15, = 5)-functionalized single-wall CNTs (// C SI la-SWNT) prepared by Alvaro et al. (2007). The functionalization process and the structure of pendant units are depicted in Figure 7.21. Attachment of such... 

For example, Dillon et al. [154] reported a covalent attachment of branched polyethyleneimine (PEI) to the sidewalls of SWNTs through the use of fluorinated single-wall CNTs as precursors. The structural integrity of the original purified SWNT is maintained upon covalent functionalization with PEI. Solid-state NMR shows the presence of carboxylate substituents due to carbamate formation as a consequence of the reversible CO2 absorption to the primary amine substituents of the PEI. Desorption of CO2 is accomplished by heating under argon at 75 °C, while the dependence of the quantity of CO2 absorbed on temperature and the molecular weight of the PEI is also observed. 

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