Purification Effect on the Electronic State of Carbon in HiPco Nanotubes

Electronic state of carbon in HiPco nanotubes before and after purification was examined using X‐ray fluorescent spectroscopy. The CKα‐spectrum of as prepared HiPco nanotubes was shown to be similar to the spectrum of graphite. The purification of carbon nanotubes by thermal and acid treatment was found to result in an enhancement of high‐energy maximum in the CKα‐spectrum. Quantum‐chemical calculation revealed such enhancement can be attributed to the sp‐hybridized carbon atoms, which are likely to compose the open tube ends and boundaries of pores developed in the tube walls during the purification.