Date of Award
Master of Science
Terry L. Miller, Qiang He
We researched effect of ambient temperature and humidity on aging of nanocarbons, including carbon nanotubes and fullerenes. We studied physicochemical properties of these nanocarbons stored in ambient conditions (20oC, 35-55%RH) for 24 months, in 90% relative humidity (RH) environment for 8 months and in 37oC environment for 13 months. We measured surface area and pore volume of samples by using N2 adsorption (77K) technique and characterized surface chemistry by using X-Ray photospectroscopy and FT-IR spectroscopy. We also analyzed structural defects with Raman spectroscopy. All tests were conducted periodically.
In ambient condition, we found that nanocarbons exhibited a trend of decreasing surface area and pore volume up to 7 to 15 months but then stabilized. We also observed a trend of decreasing surface oxygen from the beginning with much lower % oxygen observed after 12 to 15 months of aging. There was also evidence that structural-defect concentration was lowered. We conclude that nanocarbons are metastable materials, and that their aging in ambient conditions has an unexpected effect whereby oxygen leaves their surface, the structure repairs itself and they become more thermodynamically stable.
Aged nanocarbons (16 months in ambient conditions) were moved to 90% RH environment and 37oC environment. We observed that in 90% RH condition, chemisorption of oxygen and/or water to nanocarbons was enhanced and % oxygen was increased; surface area, pore volume and structural defects were reduced with a trend of approaching to equilibrium. We conclude that humidity could promote chemisorption of oxygen/water in the air to nanocarbons. We found that in 37oC condition, chemical properties of nanocarbons were only slightly decreased, but their surface area and pore volume were deceased in 1 to 3 months, and then increased in 3 to 13 months. Their physical changes may be related to the temperature dependent thermal expansion which softened intertubular interaction and enlarged spaces between tubes.
This study demonstrated that ambient temperature and humidity play important roles in aging of nanocarbons and also showed that nanocarbons possess differences from bulk carbons in aging. This study could benefit potential applications of nanocarbons and improve understanding long-term environmental impacts of nanocarbons.
Yang, Liangcheng, "Effect of Ambient Temperature and Humidity on Aging of Nanocarbons. " Master's Thesis, University of Tennessee, 2009.