Characterization of multi-walled carbon nanotubes functionalized by a mixture of HNO3/H2SO4

Multi-walled carbon nanotubes (MWCNTs) are functionalized by oxidative treatments with a mixture of nitric acid and sulfuric acid solution. Oxidation methods are reported as an effective method to functionalize the surface of MWCNTs. Although effective, a bad control of the oxidation conditions frequently causes serious modification of the structural integrity of MWCNTs. In an attempt to achieve experimental conditions which efficiently functionalize the surface of MWCNTs minimizing nanotube damage, we perform a systematic study of the influence of different oxidizing conditions on the morphological and chemical - physical properties of multi walled carbon nanotubes. Field Emission Scanning Electron Microscopy (FE-SEM) is used to study the structure and morphology of the pristine and oxidized MWCNTs. Experimental results obtained by Raman spectroscopy indicates the maintenance of the graphitic structure of MWCNTs after all oxidations. Energy dispersive X-Ray (EDX) measurements indicate that the oxygen content increased with increasing treatment time. Thermal Gravimetric Analysis (TGA) demonstrates that the treatment time of 18 h with a 1:3 mixture of 4.0 M HNO3/10.0 M H2SO4 promotes an increase in the COOH groups onto the nanotube surface (similar to 28%) with no destruction of the nanotubes. The treatment methods can be chosen as the optimal condition to perform functionalization of MWCNTs.