Carbon chemical modification/derivatization

Due to the nature of carbon materials, the presentation of representative methods for surface derivatization will follow an approach different from that described in the preceding section, which is based on the spatial target site where physical-chemical modification can take place (1) immobilization performed at edges and/or ends and defects of graphitic sheets, (2) immobilization onto the graphene sheets, and (3) exclusively for CNTs we present some examples of endohedral encapsulation of metal complexes. For the first two cases, covalent bonding and noncovalent interactions can occur directly between the transition metal complex and carbon supports or via spacers grafted to the carbon surface. 

However, research on carbon nanotubes has opened new avenues in the area of materials science and carbon surface derivatization. Their physical and chemical modifications offer excellent opportunities not only in the characterization and understanding of CNT chemistry, but also in highlighting their potential applications. In the context of this chapter, one important application of CNTs is their use as support for homogeneous catalysts in fact, based on the very few examples published in the literature, this is clearly a very promising area. Furthermore, the potential extrapolation of the CNT derivatization methodologies to more traditional and other recent carbon materials (mesoporous and ordered porous carbon materials) is also one of the major challenges for all researchers who are involved with carbon materials. 

Despite much interest in CNs, manipulation and processing of these materials has been limited by their lack of solubility in most common solvents. Many applications of CNs (mainly SWNTs) require chemical modification of the materials to make them soluble and more amenable to manipulation. Understanding the chemistry of SWNTs is critical for rational modification of their properties, and several different procedures for chemical derivatization of CNs have been described in the last four years. These methods have been developed in an effort to understand the chemical derivatization and to control the properties of these systems. There is substantial interest in studying the photophysical properties of single-walled carbon nanotube (SWNT) derivatives obtained by covalent [82] and noncovalent [83] functionalization, with the overall objective of obtaining materials with new properties [84]. Functionalization of SWNTs by covalent bonding can be achieved by two different approaches - the bonds can be formed either at the tube opening or on the lateral walls. 

A number of different approaches are underway for modifying polymers in supercritical carbon dioxide medium. These are either chemical modifications such as side group derivatization, or physicochemical modifications such as in-situ blending. 

The chemical modification by silani2a-tion (or other chemical reactions) of carbon, oxide, or metal electrode surfaces [21, 22] or SAM formation on gold surfaces with thiol or disulfide compounds [23] has been utilized for the tip functionalization. The systematic chemical derivatization of the tips was carried out with silane [10, 24-27] or thiol [17, 18, 20, 28-37] derivatives. Today, chemical differentiation of the terminal groups by FFM [5-20,28, 36, 37] or adhesive force measurements [17, 18, 20, 24-28, 30-37] is called chemical force microscopy (CFM) [17]. Adhesive and frictional forces can be mapped in x-y planes as CFM images. The adhesive... 

Most of the work on the derivatization of podophyllotoxin has targeted the C4 position. These studies can be classified according to the fate of the carbon-oxygen bond, which may be either retained or replaced by a carbon-nitrogen or a carbon-carbon bond. When retaining the C-0 bond, derivatization has involved either the modification of the sugar moiety or its replacement with groups of different chemical nature. 

A powerful strategy to covalently derivatize carbon electrodes with monolayers and multilayers utilizes electrochemical reactions (75). Electron transfer is used to activate a heterogeneous chemical reaction. The adlayer is formed after generating the highly reactive species by oxidation or reduction of the solution-based molecule or a surface-based functional group. In most electrochemically assisted modification schemes, the reaction involves a carbon radical. 

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