Nitric acid oxidation of vapor grown carbon nanofibers

Vapor grown, carbon nanofibers (Pyrograf III(TM)) with 100-300 nm diameters and similar to10-100 mum lengths were oxidized in 69-71 wt.% nitric acid (115 degreesC) for various times (10 min to 24 h). These fibers were remarkably oxidation-resistant. XPS (O-ls) 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 CO2-DR measurements exhibited an increase from 20-25 in 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 similar to3-fold increase in surface acidic functions (similar to27 to 76 mumol/g) occurring after 10 min of oxidation. Then this level remained constant through 24 h of oxidation. XPS (C-ls), O-ls) confirmed that carboxyl groups were removed and ester, anhydride, quinoid and phenolic hydroxyls appeared upon HNO3 oxidation. Oxidized fibers dispersed when shaken in water, demonstrating wettability had increased. A model for this oxidation behavior is proposed. (C) 2004 Elsevier Ltd. All rights reserved.