A method of chemically modifying carbon nanotubes having a diameter less than one micron comprising: contacting the nanotubes with a peroxygen compound selected from the group consisting of organic peroxyacids, inorganic peroxoacids and organic hydroperoxides, or a salt thereof, under oxidation conditions and thereby producing modified carbon nanotubes. Oxidation of the nanotubes increases the degree of dispersion of aggregates of nanotubes and aids in the disassembling of such aggregates. The dispersed nanotubes are used to prepare rigid structures and can be used in electrodes and capacitors.
A conductive carbon nanotube film having high tensile strength and initial tensile modulus comprises primarily oxidized small-diameter carbon nanotubes wherein the diameter of the small-diameter carbon nanotubes are at most about 3 nm. A method for making the film comprises refluxing an aqueous mixture comprising carbon nanotubes and an oxidizing agent to form a refluxed nanotube dispersion; forming a carbon nanotube film from the refluxed carbon nanotube dispersion; optionally removing nitric acid or other oxidizing agent from the carbon nanotube film; drying the carbon nanotube film; and heat-treating the carbon nanotube film to form a heat-treated carbon nanotube film. The method can also comprise sonicating the nanotubes prior to or after refluxing. A heat-treated small-diameter carbon nanotube film can have a tensile strength of over 70 MPa and an initial tensile modulus of about 5 GPa.