Nanotube Functionalization: Investigation, Methods and Demonstrated Applications

Abstract

This review presents an update on nanotube functionalization, including an investigation of their methods and applications. The review starts with the discussion of microscopy and spectroscopy investigations of functionalized carbon nanotubes (CNTs). The results of transmission electron microscopy and scanning tunnelling microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, Raman spectroscopy and resistivity measurements are summarized. The update on the methods of the functionalization of CNTs, such as covalent and non-covalent modification or the substitution of carbon atoms, is presented. The demonstrated applications of functionalized CNTs in nanoelectronics, composites, electrochemical energy storage, electrode materials, sensors and biomedicine are discussed.

Keywords: carbon nanotubes; covalent modification; filling nanotubes; non-covalent modification; substitution of atoms.

Figure 1

TEM micrograph of purified SWCNTs (a). TEM micrograph of SWCNTs after fluorination at 325 °C (b). TEM micrographs of SWCNTs after fluorination at 500 °C reveal a mixture of defective bundles (c) and MWCNTs (d). Scale bar, 10 nm. Reprinted with permission from Ref. [44]. Copyright 1998 Elsevier.

Figure 2

TEM images of samples at 100 kV: (a) control unexposed samples; (b) exposed to SF₆ at −200 V bias; (c) exposed to CF₄ at -200 V bias. Reprinted with permission from Ref. [45]. Copyright 2004 Elsevier.

Figure 3

STM images of a SWCNT (a) after fluorination at 250 °C for 12 h. The bright regions correspond to sections on the tube covered by fluorine atoms. (b) A pristine single-walled carbon nanotube was deposited on an Au (111) surface grown on mica substrate and imaged with a C60-functionalized STM tip. The image is high-pass filtered Reprinted with permission from Ref. [46]. Copyright 2002 Elsevier.

Figure 4

(a) C 1s XPS spectra of pristine SWCNTs and SWCNTs fluorinated at 150, 200, 250 and 300 °C. (b) Gaussian peak fitting of the C 1s XPS spectra of the SWCNTs after fluorination at 300 °C. The individual peaks are due to sp² (A), sp³ (B), oxygen bonds (C–E) and fluorine bonds (F–H). (c) F 1s XPS spectra of the same fluorinated SWCNTs. (d) Atomic F/C ratio versus fluorination temperature Reprinted with permission from Ref. [47]. Copyright 2002 Elsevier.

Figure 5

FTIR spectra of pristine SWCNTs and SWCNTs fluorinated at 150, 200, 250 and 300 °C. Reprinted with permission from Ref. [48]. Copyright 2003 Elsevier.

Figure 6

The Raman spectra of the pristine SWCNTs and the nanotubes fluorinated at 150, 200, 250 and 300 °C. The inset shows the dependence of the intensities of G and D modes on the doping temperature. Reprinted with permission from Ref. [48]. Copyright 2003 Elsevier.

Figure 7

(a) Raman spectra of control and CF₄ plasma exposed single-walled CNTs. (b) The deconvoluted F 1s peak for the SF₆ and CF₄ plasma exposed SWCNTs at −200 V for 1 min in comparison to the unexposed control sample. Reprinted with permission from Ref. [49]. Copyright 2004 Elsevier.

Figure 8

Centrifuge tubes after DGU separations using Pluronic F108 (top) and Pluronic F68 (middle) are shown in pictures. Optical absorbance spectra of the SWNTs that were extracted in the centrifuge tube at the locations shown by arrows [188]. The colors of CNTs represent their color in suspension.

Figure 9

Photographs of various CNT dispersion in dilute epoxy solution (xylene-butanol (1:1) mixture) when the mixture was allowed to settle for 6 h. From left to right: CNT-ODA; CNT-OH; CNT-COOH and CNT-raw Copyright 2010, American Chemical Society. Reprinted with permission from Ref. [193]. Copyright 2004 American Chemical Society.

Figure 10

(a) Rate performance at a current density ranging from 100 to 1000 mA/g of SnO₂@CNTF and (b) relative values of the capacity [196]. Colours showed different specific capacities.

Figure 11

(a) The cyclic voltammograms of MWNTs/Au-Ag/GCE (butanone was varied from a to h: 0, 0.05, 0.1, 0.15, 0.25, 0.35, 0.45 and 0.55 ppm, respectively). (b) The cyclic voltammograms of MWNTs/Au-Ag/GCE under different concentrations of 3-octanone (varying from a to f: 0, 0.05, 0.1, 0.15, 0.2 and 0.25 ppm, respectively). The inset shows a line plot of the peak current (Ip) against the concentration of butanone and 3-octanone [206].