Acid Functionalization of Carbon Nanofibers

We have studied the effects of temperature (70-100A degrees C), process duration (1-4 h), and the ratio of the acid mixture (concentrated HNO3 and H2SO4 in the volume ratio 1: 3) volume to carbon nanofiber weight (70: 1 to 133: 1 ml/g) on the yield of functionalization products and their dispersibility in water. The results indicate that, with increasing temperature and process duration, the yield of functionalization products decreases, and their concentration (solubility) in the aqueous dispersion increases: from 1.2-1.3 to 11.0 mg/ml when the yield decreases from 71-89 to 30%. We present the first measurements of the gas volume evolved during functionalization and show that it increases with increasing temperature and process duration, reaching 500-600 ml/g carbon under the most severe conditions. The major component of the reaction gases is CO2 (over 50 vol %).