Abstract
We studied the physicochemical properties of several commercially available single- and
multi-walled carbon nanotubes (SWNTs and MWNTs) and fullerenes stored in normal ambient
conditions for 24 months. We found that SWNTs exhibit a trend of decreasing surface area and
pore volume up to 7 to 15 months but then stabilized, no longer being impacted by sample age or
outgassing temperatures. Using X-ray Photoelectron Spectroscopy, we also observed a trend of
decreasing surface oxygen in all samples from the beginning with much lower % oxygen
observed after 12 to 15 months of aging under ambient conditions. The surface oxygen then
stabilized for the duration of this study. There was also evidence that the total structural-defect
concentration, estimated from Raman spectroscopy, was somehow lowered during the aging
process. The decrease in surface oxygen is an unexpected phenomenon because most other
carbons, such as activated carbons or carbon molecular sieves, either oxidize or remain
unaffected by age. We believe that nanocarbons are meta-stable materials (in pseudo-thermodynamic equilibrium), and that their aging in ambient conditions makes them
more thermodynamically stable with fixed properties. This new information about the properties
of nanocarbons should be further explored as it can help resolve some of the conflicting reports
such as those about the environmental impacts of nanomaterials.
