Bulk separative enrichment in metallic or semiconducting single-walled carbon nanotubes

A postsynthesis method of separating metallic from semiconducting single-walled carbon nanotubes and a method based on absorption spectroscopy for assay of the separation efficiency are described. The separation method relies on chemical discrimination in the charge-transfer complex formation between bromine and the metallic versus semiconducting nanotubes and takes advantage of the resulting density difference to effect a centrifugation-based separation. Calculations support the proposed separation mechanism.