Carbon Nanotube Purification

Development of carbon nanotubes (CNTs), including single-wall and multi-wall nanotubes and nanofibers, into useful devices requires fabrication of CNTs that are relatively free from process residues such as amorphous carbon and metallic particles that are not part of a CNT array grown on a (coated) substrate. Conventional techniques for removal of amorphous carbon and other residues often use one of several techniques. One technique uses post-growth thermal or plasma cleaning of the amorphous carbon with Ox (x=2), which non-selectively attacks the CNT material as well as the amorphous carbon. Metal contaminants are removed using an acid bath, which is again a non-selective process and requires disposal of the strong acids and contaminant removal byproducts. A second technique uses certain toxic gases, such as halogens, to remove the amorphous carbon and other residues. This approach requires disposal of one or more hazardous substances and often requires many hours to complete. A third approach requires holding the amorphous carbon and CNTs in a heated Ox atmosphere for several hours, in order to limit the damage to the CNTs.