A new method was described for labeling the defects of single-walled carbon nanotubes, using TiO2 nanoparticles as markers. Single-walled carbon nanotubes were prepared by chemical vapor deposition, and dilute nitric acid (2.6M) oxidation was used to introduce carboxylic acid groups at the defect sites. Characterization of the single-walled carbon nanotubes using ultra-structural and spectroscopic analyses was carried out following the introduction of TiO2 nanoparticles. The results indicated that TiO2 nanoparticles were chemically absorbed at single-walled carbon nanotube defect sites via an ester-type linkage between carboxylic acid groups at the defect sites and hydroxyl groups at the surface of the TiO2 nanoparticles. In addition, the adsorption behavior of TiO2 nanoparticles on single-walled carbon nanotubes was determined following oxidation of the single-walled carbon nanotubes using various processes. The results indicated that gas-phase oxidation introduced very few defect sites, as revealed by the low adsorption density of TiO2 nanoparticles. Refluxing in dilute nitric acid was considered to be a mild oxidation method for single-walled carbon nanotubes; affecting only those defects already present and causing no further damage. In contrast, sonification of single-walled carbon nanotubes in H2SO4/H2O2 increased the incidence of carboxylic acid groups, not only at original defect sites but also at newly created defect sites along the walls of single-walled carbon nanotubes, resulting in a higher density of TiO2 nanoparticles. Labeling of single-walled carbon nanotube defect sites using TiO2 nanoparticles permitted direct determination of the density, distribution and location of the defects and offered new possibilities for the creation of heterojunctions between nanotubes and nanoparticles.

Labeling the Defects of Single-Walled Carbon Nanotubes using Titanium Dioxide Nanoparticles. X.Li, J.Niu, J.Zhang, H.Li, Z.Liu: Journal of Physical Chemistry B, 2003, 107[11], 2453-8