Noncovalent Attachment of Functional Units

The interaction between the it-systems of the aromatic compound and the nanotube is based on an overlap of the respective orbitals. Bent graphene layers, as already stated in the chapter on fuUerenes, exhibit a curved it-system. On the one hand, this has an influence on the degree of electron delocaUzation, while on the other hand it sets a Umit to the overlap with planar aromatic compounds. Contrary to fuUerenes, however, the nanotubes are not curved in aU three directions in 

The reaction with pyrene is largely established as fundamental example for this kind of noncovalent functionalization for several reasons. Firstly, it allows for a wide scope of derivatization, secondly, it can be aligned in parallel with the tube s axis, and finally, the solubihty of pyrene compounds ensures an easy handling. In fact, larger aromatic systems already give rise to similar solubihty problems like fuUerenes or nanotubes themselves. 

An interesting idea would thus consist in a functionalization with aromatic compounds bent around the z-axis. These should interact especially well with the 7t-system of the nanotubes, possibly even featuring certain selectivity for nanotubes with different diameters. A first attempt of this kind has been presented just recently. A belt-shaped aromatic molecule has been put over a fullerene here (refer to Section 2.5.6). Such a procedure should in principle be applicable to nanotubes as well. A success in performing this reaction would mean a big step toward a size-selective functionalization and possibly even toward a directed separation of individual species. Here an interaction with aromatic compounds immobilized within tubular templates, for example, within zeolites, would be another conceivable strategy. 

Further Noncovalent Derivatizations of Carbon Nanotubes By now there are numerous different approaches to derivatizing single- and multiwalled carbon nanotubes by way of noncovalent interactions. A multitude of further organic or inorganic substances can be bound to nanotubes besides those mentioned above. 

Pure metals as well can be deposited on the surface of carbon nanotubes. The reductive precipitation of gold nanoparticles on MWNT coated with citrate ions may be given just as one example. Besides dispersing the MWNT, the citric acid is also responsible for the reductive generation of the gold particles from HAuCLt. Other metals like platinum, palladium, titanium, and iron can be deposited on the nanotube surface, too. 

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