Stability of multi-walled carbon nanotubes in commonly used acidic media

Multi-walled carbon nanotubes (MWCNT) were treated in five commonly used acidic media with different pKa values. The stability of the MWCNT was evaluated by using various characterization techniques. The results indicated that oxidative damage of MWCNT was not closely related to acid strength, and that the MWCNT was more sensitive to the oxidizing nature of the acid. As a result, the MWCNT treated with the strongest acid, trifluoromethanesulfonic acid (pKa = −15.9), only reached oxygen content of 1.8%, while nitric acid (pKa = −1.5)/sulfuric acid (pKa = −3.0) treated MWCNT showed oxygen content as high as 19% after 24 h treatment. The remaining acidic media did not noticeably increase the oxygen content of the MWCNT up to 24 h treatment.