Functionalizing multi-walled carbon nanotubes using ECR plasma and a mild nitric acid treatment

In the present work, a two-step process combining electron cyclotron resonance (ECR) plasma and 0.25 M nitric acid treatments is utilized to functionalize multi-walled carbon nanotubes (MWCNTs). In the process, high density and high incident energy hydrogen and oxygen cations generated by using ECR plasma system are used to bombard the MWCNTs for 5 min to break C-C bonds, creating free radical defects on the nanotube surface; the treated nanotubes are subsequently sonicated in the mild acid for 2 h, forming functional groups at the defects. Several characterization techniques, including X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy, and thermogravimetric analysis, are utilized to systematically evaluate the effect of the method. The results show that the MWCNTs treated by the presented method can contain a high concentration of oxygen-containing functional groups on the nanotube surface with the added advantage of high thermal stability and minimal destructive effects to the material structure.