An easy method for direct metal coordination reaction on unoxidized single-walled carbon nanotubes

The transition metal copper (II) ion (Cu²⁺) was effectively coordinated with a single-walled carbon nanotube (SWCNT) to produce a SWCNT–Cu²⁺ complex by a metal coordination reaction. Since the complex was very reactive towards the carboxylic acid group, the chemical functionalization of SWCNTs was easy to accomplish. This approach was used to functionalize the surface of the SWCNTs with stearic acid or ethylenediaminetetraacetic acid for tuning of the relative hydrophobicity and hydrophilicity of the surface, respectively. The mild reaction conditions used for metal coordination of the SWCNTs minimized the defects that result from chemical modification of SWCNT. Thus, the electrical properties of unmodified SWCNTs were preserved. Various analytical techniques, including Fourier transform infrared spectroscopy, thermal gravimetric analysis, ultraviolet–visible spectroscopy, and water sorption isotherm measurements, were used to characterize the surface properties of the functionalized SWCNTs. Functionalization of SWCNTs by metal coordination reaction effectively modified the SWCNT surface, while conserving the excellent physical properties of the SWCNTs. The surface properties of the SWCNTs were easily tuned by introduction of the functional groups required for specific applications.