XE-129 NMR-SPECTROSCOPY OF XENON GAS ADSORBED ON AMORPHOUS CARBONS

Abstract

Xe-129 NMR spectra of xenon gas adsorbed on amorphous carbons have been obtained under various pressures up to 1 atm at 296 K. The chemical shift thus obtained has been found to be a linear function with respect to the surface concentration of the adsorbed xenon. The value of the chemical shift extrapolated to zero concentration is clearly increased when acidic functional groups are present on the carbon surface, indicating that the Xe-129 NMR spectroscopy can be a sensitive probe for the characterization of the amorphous carbon. However, the plot of the xenon chemical shift versus the xenon concentration for a number of samples having different specific surface area and pore-size distribution gives a very similar slope. This can be explained by the xenon-xenon interaction term for the chemical shift which results mostly from the interaction between the adsorbed xenon atoms on the surface. By varying the carbon particle size, a very large line broadening in Xe-129 NMR spectra of amorphous carbons is also shown to occur arising from the inhomogeneity of such particles.