Multi-wall carbon nanotubes: Purification, morphology and field emission performance

Highly pure multi-wall carbon nanotubes (MWNTs) were successfully fabricated using an acidic purification process. Treatment with acids, concentrated sulfuric acid (H2SO4) and nitric acid (HNO3) eliminated many of the metal catalysts and impurities from MWNTs. The concentration of H2SO4/HNO3 solution and the purification time were optimized. Experimental data demonstrate that a 1:3 concentrated H2SO4:HNO3 solution after 20 h yields highly pure MWNTs. MWNTs were closed tips that are opened after purification. The intensity ratio of the D band to the G band (ID/IG) is as low as 0.27. The field emission current density is as high as 170 μA/cm2 at an electric field of 1.9 V/μm.