The present invention relates to a method of preparing purified carbon nanotubes (CNTs) comprising mixing starting CNTs with an organic solvent in the presence of sonication; substantially removing the organic solvent to obtain a CNT composition; and heating the CNT composition at 200° C. or higher to obtain the purified carbon nanotubes. The present invention further relates to the purified CNTs and cohesive CNT assemblies prepared from the method described herein, and articles (e.g. capacitor, energy storage device or capacitive deionization device) comprising the purified CNTs.