Bifunctional Carbon Nanotubes by Sidewall Protection


  • The authors thank Rodney Andrews and Dali Qian the Center for Applied Energy Research (Univ. of KY) for supplying MWCNTs. The Center for Micro-Magnetic Electronic Devices and Electron Microscopy Center at Univ. of Kentucky provided critical equipment infrastructure. Sponsorship was provided by Air Force Office of Scientific Research (DEPSCoR program) under agreement #F49620-02-1-0225 and NSF CAREER award (CTS-0348544).


A vertically aligned array of multiwalled carbon nanotubes (MWCNTs) impregnated with polystyrene is utilized to independently functionalize each end of the MWCNTs. The presence of the polystyrene matrix prevents sidewall oxidation of the CNTs, resulting in carboxylate derivatization at the CNT tips during processing via plasma oxidation. The membrane is subsequently dissolved in toluene, resulting in a suspension of CNTs with carboxylate-derivatized tips. The CNT tips are further functionalized using carbodiimide-mediated linking of carboxylate at the CNT tips with an amine of 2-aminoethanethiol. This treatment results in thiol functionality and Fourier-transform infrared (FT-IR) studies confirm amide-bond formation. Gold nanoparticles that are readily observed using transmisison electron microscopy (TEM) are then covalently linked to the thiol functional groups. Estimates of the average nanoparticle density are observed to decrease from ∼ 526 particles μm–1 near the CNT tips to negligible values (< 7 particles μm–1) at locations beyond 700 nm from the CNT tips. This is consistent with a membrane geometry where CNTs tips are above the polystyrene surface owing to differing oxidation rates. Bifunctional CNTs (with different chemical functionality at either end of each CNT) is achieved by thiol functionalization on only one side of the oxidized CNT membrane floating on top of a 2-aminoethanethiol functionalization reaction solution. After dissolution of the polystyrene matrix, TEM analysis shows gold-nanoparticle decoration at the thiol-functionalized end of the CNT.