(72e) Characterization of Nanoporous Carbon by Water Adsorption

Microporous carbon molecular sieves, which contain pores of size less than 1 nm, are characterized by water adsorption in this study. Isotherms are obtained over a wide range of concentration from around 0.1 % to 90% of the vapor pressure and multiple temperatures are probed. Isotherms are characterized by application of the extended cooperative multimolecular sorption theory which decomposes the observed isotherm into two distinct modes of adsorption. Saturation capacities and isosteric heats of water adsorption are obtained, compared with other probe molecules and subsequently used to characterize the carbon molecular sieve. A lack of observable difference between the equilibrium adsorption and desorption isotherms, coupled with the results of equilibrium pressure shift displacement experiments, provides indication of the absence of hysteresis. The pressure shift displacement experiments conducted with carbon dioxide at various concentrations of pre-adsorbed water, reveal significant blocking of carbon dioxide from the micropores. A quantitative description that is consistent with the water adsorption model, and that describes the blocking over a wide range of water concentrations, is proposed and successfully applied to characterize the data. LAUR-06-2854