The Influence of Nitric Acid Treatment on the Crystallographic Structure of Multiwalled Carbon Nanotubes

Commercially available Multiwalled Carbon Nanotubes (MWCNTs) were refluxed with nitric acid in order to improve the density of the acidic surface functional groups. The formation of oxygen containing functional groups may lead to surface enhancement of MWCNTs for further modifications. The crude MWCNTs were refluxed in nitric acid at 100 °C for time ranging between 3 to 24 h. The influence of treatment time on crystalline structure was investigated using X-Ray Diffraction (XRD); the results confirmed that all treated MWCNTs are crystalline. The density of the surface functional groups on treated MWCNTs was examined by Fourier Transform Infrared (FTIR). The FTIR spectrums revealed a strong vibration band at 1739, 1219, 1369 cm-1 that indicates covalently bound acidic surface functional groups existed on the treated MWCNTs. The amount of acidic groups increased with the reflux time up to 15 h treatment as measured by an acid-base Boehm titration. The vibrational spectroscopy of these functional groups also increased with the increasing reflux time.