The superiority of air oxidation over liquid-phase oxidative treatment in the purification of carbon nanotubes

Questions of fundamental importance to the purification of carbon nanotubes (CNTs) have been investigated. We contrast the oxidation of CNTs in air with the overwhelmingly popular liquid-phase oxidising acid-treatment, and find that the former is advantageous over the latter, while being at least as efficient. Air-oxidation can remove the associated impurities in as-produced CNT material while inflicting considerably less damage than oxidising acid-treatment, and also does not lead to the formation of debris on CNT surfaces. Air oxidation may be inevitable in CNT purification, even if liquid-phase oxidation has been employed. It was also found that there is no "standard" recipe for purifying CNTs, even for different batches produced by the same method while keeping the macroscopic process conditions identical; purification procedures must be re-evaluated for every batch to ensure complete removal of impurities. (C) 2011 Elsevier Ltd. All rights reserved.