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In order to optimize applications of carbon materials, a comprehensive characterization with regard to their surface area, pore volume/size distribution, etc. is required. For this task, gas adsorption can be considered a standard technique, because it allows for assessing a wide range of pore sizes. High resolution adsorption experiments with (preferably) argon at 87 K or nitrogen at 77 K coupled with CO2 adsorption at 273 K has become a standard tool for the assessment of microporous carbons. Pore filling of narrow micropores (< 0.7 nm) with nitrogen or argon at cryogenic temperatures occurs at very low pressures (< 100 mTorr) and coupled with these low pressures and temperatures is the well-known problem of restricted diffusion, which prevents nitrogen and argon molecules from entering the narrowest micropores, i.e. pores of width < 0.45 nm. In order to address this, the use of CO2 as adsorptive at temperatures close to room temperature (i.e. 273 K) has been suggested which allows one to overcome such diffusion limitation and to obtain reliable pore size and volume information of the most narrow pores. With regard to the analysis of the adsorption data, it has been shown that methods for pore size analysis based on non-local density functional theory (NLDFT) and molecular simulation lead to reliable pore size and volume information over the complete range of micro- and mesopores. These methods are available for many different adsorptive/adsorbent pairs and are also featured in international standards such as ISO standard ISO 15901-3. More recent advances include the development of quenched solid density functional theory (QSDFT), which quantitatively takes into account the surface geometrical inhomogeneity characterized by a roughness parameter. It has been demonstrated that QSDFT significantly improves the accuracy of the pore size distribution for many micro- and mesoporous carbons. Instruments; all manometric (volumetric) Quantachrome sorption analyzers: |
