The efficiency of the oxidation of carbon nanofibers with various oxidizing agents

The oxidation of carbon nanofibers (CNFs) with various oxidizing agents; 6 M HNO₃, KMnO₄, RuO₄, and a mixture of concentrated H₂SO₄/HNO₃ is studied to determine the reaction conditions that optimizes yield and chemical functionalization. The oxidized nanofibers were examined by scanning electron microscopy, and Raman spectroscopy to characterize the defects caused by oxidation. The amount of acidic sites generated during oxidative treatment was quantified by reacting them with amine terminated octadecane and the subsequent quantification of the products of this grafting process by Fourier transform infrared spectroscopy. The concentrated H₂SO₄/HNO₃ mixture created the maximum number of carboxylic acid groups and the highest amount of defect sites, but had very low yield (∼12%). Six molar of HNO₃ generated fewer defect sites and a lower number of -COOH groups, but did exhibit a 70% yield. RuO₄ and KMnO₄ resulted in similar amounts of overall defect sites, however the yield and amount of -COOH groups for KMnO₄ treated CNF were significantly lower than the RuO₄ treatment. Overall, oxidation of these CNF with RuO₄ provides the best balance of yield and carboxylation.