Enrichment of Metallic Single-Walled Carbon Nanotubes with Simultaneous Purification by Nitric Acid Treatment

Abstract

Controlled treatment of pristine single-walled carbon nanotubes (SWCNT) with HNO₃ (11 M) for 20 hours at 50°C with subsequent repeated cycles of washing, centrifugation and ultrasonication in aqueous media have shown enrichment of the product with pure and debundled nanotubes of metallic variety. On the other hand, no such enrichment was observed when the tubes were treated with a mixture of concentrated nitric acid and sulfuric acid. The electrical varieties of the tubes were ascertained from the analysis of Raman and UV-Vis spectra and dc-resistivities. The purity of the product was gauged from transmission electron microscope images, energy dispersive spectra, thermogravimetric analysis and Raman spectra. A mechanism involving preferential attack of NO₃⁻ on the semiconducting tubes under the condition of the adopted protocol has been proposed from the comparison of the results after the treatment of the same pristine SWCNT with mixed acid (conc. HNO₃ and H₂SO₄).

Keywords::

• nanostructures
• enrichment
• Raman spectroscopy
• SWCNT
• electrical properties

Additional information

Funding

Council of Scientific and Industrial Research (CSIR), India for the financial support for the work and fellowship provided to one of the authors (Amrita Chakravarty) is acknowledged.