Displacement ofCO2by Xe in single-walled carbon nanotube bundles

Abstract

The displacement of $\mathrm{C}{\mathrm{O}}_{2}$ by Xe on single-walled nanotube bundles is investigated with Fourier transform infrared spectroscopy (FTIR) and grand canonical Monte Carlo (GCMC) simulations. The FTIR experiments show that $\mathrm{C}{\mathrm{O}}_{2}$ physisorption at $77\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ produces an infrared peak at $2330\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ for endohedral physisorption and at $2340\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ for groove/external surface physisorption. Exposure to Xe causes a sequential displacement of $\mathrm{C}{\mathrm{O}}_{2}$ from these sites as shown by an intensity loss of the $2330\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ peak, which precedes the loss at $2340\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. The GCMC simulations on heterogeneous and homogenous bundles show that $\mathrm{C}{\mathrm{O}}_{2}$ in endohedral sites is initially displaced by Xe before that in groove/external surface sites. The $\mathrm{C}{\mathrm{O}}_{2}$ populations in each site of the bundle are taken from the GCMC simulations and used to model the variation of the FTIR intensities as a function of Xe pressure. The qualitative agreement between the simulated and experimental intensity changes is good, suggesting that the intensity changes seen in the experiments are related to $\mathrm{C}{\mathrm{O}}_{2}$ displacement from the sites indicated in the simulations.