J. Phys. Chem. B 2002, 106, 8671-8675
8671
Purification of Single-Wall Carbon Nanotubes by Selective Microwave Heating of Catalyst Particles Avetik R. Harutyunyan,*,†,§ Bhabendra K. Pradhan,† Jiping Chang,‡ Gugang Chen,† and Peter C. Eklund† Department of Physics, 104 DaVey Laboratory, The PennsylVania State UniVersity, UniVersity Park, PennsylVania 16802, and Materials Research Laboratory, The PennsylVania State UniVersity, UniVersity Park, PennsylVania 16802 ReceiVed: April 28, 2002
A new scalable method for purification of single-wall carbon nanotubes (SWNTs) by using microwave heating in air is developed. The microwaves couple to the residual metal catalyst, raising significantly the local temperature leading to both the oxidation and rupturing of the carbon passivation layer over the metal catalyst particles. With this protective carbon coating weakened or removed, a mild acid treatment is then sufficient to remove most of the metal in the sample, leaving the nanotubes in tact. Using microwave processing and 4 M HCl acid reflux for 6 h we were able to remove residual metal (Ni, Y) in arc-discharge SWNTs to a level lower than 0.2 wt % (∼0.04 at. %). Results from transmission and scanning electron microscopy, Raman spectroscopy, and thermogravimetric studies were discussed.
Introduction Single-wall carbon nanotubes (SWNTs) were first reported by Iijima and co-workers at NEC, and Bethune and co-workers at IBM in 1993.1,2 Most of the synthesis methods today produce tubes in the diameter range 1-2 nm, and they are arranged in bundles of ten to hundreds of tubes. SWNTs are often a minority constituent (
