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.