129Xe NMR spectroscopy of adsorbed xenon: Possibilites for exploration of microporous carbon materials

Despite the extensive use of Xe-129 NMR for characterization of high surface-to-volume porous solids, particularly zeolites, this method has not been widely used to explore the properties of microporous carbon materials. In this study, commercial amorphous carbons of different origin (produced from different precursors) and a series of activated carbons obtained by successive cyclic air oxidation/pyrolysis treatments of a single precursor were examined. Models of Xe-129 chemical shift as a function of local Xe density, mean pore size, and temperature are discussed. The virial coefficient arising from binary xenon collisions, sigma(Xe-Xe), varied linearly with the mean pore size given by N-2 adsorption analysis; sigma(Xe-Xe) appeared to be a better probe of the mean pore size than the chemical shift extrapolated to zero pressure, sigma(S).