Carbon nanotubes (CNTs) were Œrst discovered in 1991 . A CNT is deŒned as a sheet of carbon atoms rolled up into a tube with a diameter in the order of tens of nanometers. Researchers all over the world have attempted to obtain puriŒed single or multiwalled carbon nanotubes. Multiwalled carbon nanotubes (MWNTs) are comprised of several concentric cylinders of graphite sheets, with an approximately 3.4 Å spacing between layers. MWNTs usually have a diameter in the order of 2-100 nm (typically 2-10 nm in internal diameter), which is slightly larger than that of a single layer cylindrical graphite sheet of single-walled carbon nanotubes (SWNTs), which is approximately 0.2-2 nm in diameter. The length of the CNTs can vary from micrometers to centimeters, giving them a very high aspect ratio (length to diameter).