P. Lakshminarayanan, H. Toghiani, C. Pittman
2004
Citations
4
Influential Citations
288
Citations
Quality indicators
Journal
Carbon
Abstract
Abstract Vapor grown carbon nanofibers (Pyrograf III™) with 100–300 nm diameters and ∼10–100 μm lengths were oxidized in 69–71 wt.% nitric acid (115 °C) for various times (10 min to 24 h). These fibers were remarkably oxidation-resistant. XPS (O 1s ) showed that the surface atomic oxygen percent increased from 6.3 to 18.3–22.5% for 10–90 min oxidations followed by a drop to 14–15% after 10–24 h oxidations. No damage was observed by TEM. Little change in surface area was observed by N 2 BET but CO 2 -DR measurements exhibited an increase from 20–25 m 2 /g to 41–73 m 2 /g after 10–90 min of oxidation followed by a decrease to 35–22 m 2 /g after 10 h, consistent with the XPS findings. Shallow ultramicropore formation could account for the surface area increase. NaOH titrations showed ∼3-fold increase in surface acidic functions (∼27 to 76 μmol/g) occurring after 10 min of oxidation. Then this level remained constant through 24 h of oxidation. XPS (C 1s ), O 1s ) confirmed that carboxyl groups were removed and ester, anhydride, quinoid and phenolic hydroxyls appeared upon HNO 3 oxidation. Oxidized fibers dispersed when shaken in water, demonstrating wettability had increased. A model for this oxidation behavior is proposed.