Intercalation and partial exfoliation of single-walled carbon nanotubes by nitric acid

Single-walled carbon nanotubes (SWNTs) were reacted with HNO3 solution. An expansion of the inter-nanotube spacing and increase in the amount of hydrogen in the material were observed by X-ray diffraction and proton NMR measurements after the SWNTs were immersed into the HNO3 solution for less than 2 hours. The change in diffraction pattern was reversible, indicating intercalation of HNO3 into the SWNT bundles. When the SWNTs were immersed in the HNO3 solution for a longer period of time, the bundles became disordered and partially exfoliated. Isolated SWNTs and large nano-particles were often observed.