AVS 50th International Symposium
    Applied Surface Science Monday Sessions
       Session AS-MoA

Paper AS-MoA1
Vibrational Behavior of Adsorbed CO@sub 2@ on the Interior and Exterior Surfaces of Carbon Nanotubes: An Experimental and First Principles Study

Monday, November 3, 2003, 2:00 pm, Room 324/325

Session: Nanotube and Nanoparticle Characterization
Presenter: W.-L. Yim, University of Pittsburgh
Authors: W.-L. Yim, University of Pittsburgh
O. Byl, University of Pittsburgh
P. Kondratyuk, University of Pittsburgh
J.K. Johnson, University of Pittsburgh
J.T. Yates, Jr., University of Pittsburgh
Correspondent: Click to Email
We have used CO@sub 2@ as a probe for the adsorption sites on single-walled carbon nanotubes (SWNTs). CO@sub 2@(g) shows an intense infrared band at 2349 cm@super -1@, due to the asymmetric CO@sub 2@ stretching mode. When CO@sub 2@ is adsorbed on (10,10) nanotube surfaces, this mode should be red shifted to a lower vibrational frequency. We measured the infrared spectrum of CO@sub 2@ adsorbed on SWNTs and have observed absorption peaks at 2341 cm@super -1@ and 2329 cm@super -1@. After ozone treatment and annealing in vacuum to 823 K, CO@sub 2@ adsorption causes the mode at 2329 cm@super -1@ to increase dramatically in intensity, with the peak at 2341 cm@super -1@ less affected. We have performed density functional calculations using the local density approximation on (10,10) SWNTs, with CO@sub 2@ adsorbed on interior, exterior, groove, and interstitial sites of bundles of the nanotubes. The CO@sub 2@ in the groove site and in the nanotube interior exhibit vibrational red shifts of 20.9 cm@super -1@ and 23.2 cm@super -1@, respectively, for the asymmetric stretching mode. This agrees very well with the experimental results for the larger shift. The CO@sub 2@ on the nanotube exterior has a theoretical red shift of 14.8 cm@super -1@ from the gas phase CO@sub 2@ mode, which may contribute to the peak at 2341 cm@super -1@ in the experiments. We have monitored the replacement of CO@sub 2@ by Xe through a series of co-adsorption experiments. Xe selectively replaces the CO@sub 2@ species giving the mode at 2329 cm@super -1@ and assigned to CO@sub 2@ bound inside the nanotubes. Thus, both experiments and simulations indicate that the more red-shifted absorption peak is due to CO@sub 2@ adsorbed on the inside and possibly the groove sites of the SWNT bundles. This work was supported by the Army Research Office.