The impact of mesoporosity on microporosity assessment by CO_2 adsorption, revisited

摘要

The use of both CO_2 and N_2 physisorption measurements provide complementary information on the determination of micropore characteristics. The presence however of a substantial amount of external surface area, as e.g. present in hierarchically structured porous materials, can lead to an overestimation of the Dubinin-Radushkevich micropore volume as derived from CO_2 physisorption. A simplified method of correction to the already known isotherm subtraction approach is proposed here. This proposed correction is proportional to the amount of external surface area determined by N_2 adsorption and is based on correction of the DR-results. Advantages of this method are the ease of determining the correction factor and the simplicity of correction the obtained micropore volume under normal conditions using only sub-atmospheric CO_2 and N_2 adsorption measurements. The results of our method show a good similarity to the isotherm subtraction approach in the obtained micropore volumes. Novel adsorption models such as Density Functional Theory can only properly take into account the contribution of the external surface area if this has been actually measured during the analysis, which requires high-pressure CO_2 adsorption.