Purified MWCNTs were characterized by transmission electron
microscopy (TEM) on carbon coated copper grid in Philips
CM-20 TEM. Fig. 1 shows the TEM picture of purified and carboxyl
functionalized MWCNTs. High resolution picture in the
inset shows the ‘‘crystalline’’ nature of the inner shells of
MWCNTs while outer shells are significantly damaged by
the oxidation treatment. TEM image analysis gives a diameter
distribution between 10 and 20 nm.