Covalent Sidewall Functionalization of Carbon Nanotubes by a “Formation−Degradation” Approach

A diazonium salt-based strategy is employed to form a covalently attached multilayer of diphenyl disulfide on the surface of single-walled carbon nanotubes (SWCNTs) or multiwalled carbon nanotubes (MWCNTs). The interlayer S−S bonds are subsequently degraded reductively to produce essentially a single layer of thiophenols (or closely related derivatives) on the nanotube surface. The functionalization is achieved in what is effectively a one-pot procedure since the involved transformations are performed without intermediate workup. This “formation−degradation” modification approach is unique in the sense that it allows the generation of a thin well-defined molecular layer in spite of the involvement of highly reactive radicals in the first step. Transmission electron microscopy and thermogravimetric analyses support the approach proposed and reveal that a significant initial functionalization is achieved. In UV−vis spectroscopy, the disappearance of the Van Hove singularities of the SWCNT after the reaction is consistent with a covalent sidewall functionalization. Moreover, the resulting thin layer of thiophenols is reactive forming Au−S bonds with a macroscopic Au surface. Finally, the peripheral thiophenol groups of the MWCNT are employed as chemical linkers for anchoring gold nanoparticles and rods in a site-selective manner.