Aqueous Solution Surface Chemistry of Carbon Nanotubes

Since the rediscovery of carbon nanotubes (CNTs) by Iijima in 1991, a plethora of applica‐ tions have been developed in the fields of biomolecular science, catalysis, environmental chemistry and medicine. Relevant to the development of these new technologies, it is impor‐ tant to effectively characterize and tune the chemical and electronic structures of these mate‐ rials for desired properties. Within the last 15 years, an array of surface characterization methods have been developed to assay the surface structures of single(SWNTs) and multiwalled (MWNTs) carbon nanotubes, in particular as organic moieties and catalytically active metal nanoparticles are tethered to them. Distinctive physical, chemical, electrical and high thermal properties of CNTs make these materials suitable for widespread applications, such as fuel cells, semiconducting materials in electronics, atomic force microscopy probes, mi‐ croelectrodes, adsorbents to remove pollutants from waste water, electrochemical sensing and drug carriers. Aqueous surface chemistry plays a vital role in determining the fate and transport of CNTs. A large fraction of the atoms in CNTs reside at or near the surface (Sayes et al., 2006; Bottini et al., 2006). Pristine carbon nanotubes are barely soluble in liquids. To introduce nanotubes in more easily dispersible forms, they require functionalization. These processes entail attaching various organic moities to the sidewalls, which can be used to tether catalytically reactive nanoparticles. Biomolecules require electron mediators to pro‐ mote electron transfer needed for effective biosensing (Sampath et al., 1998). Electrochemical metal ion sensors require certain functional groups which show potential affinity towards particular metal ions (Mojica et al., 2007). Surface electrostatic interactions in solution also influence the sorption properties of these materials to entrain environmental contaminants on the CNT sidewalls (Tavallai et al., 2012).