Assessment of microporosity

Stoeckli HF, Rebstein P, and Ballerini L. On the assessment of microporosity in active carbons, a comparison of theoretical and experimental-data. Carbon, 1990 28(6) 907-909. 

Another procedure which may be used for the assessment of microporosity is the preadsorption method. In this approach the micropores are filled with large molecules (e.g. nonane), which are not removed by pumping the adsorbent at ambient temperature. In the most straightforward case, this procedure can provide an effective way of isolating the micropores and leaving the external surface available for the adsorption of nitrogen, or another suitable adsorptive. 

Assessment of microporosity from adsorption of organic molecules of different shapes and sizes is examined in Chapter 8. 

Determination of the polarity of solid surfaces 135 Study of surface modification 137 Assessment of the site-energy distribution 138 Assessment of structural modifications of the adsorbent 139 Assessment of microporosity 139 Assessment of surface area 139... 

Kruk, M., Jaroniec, M., and Choma, J. (1998). Comparative analysis of simple and advanced sorption methods for assessment of microporosity in activated carbons. Carbon, 36, 1447-58. 

Stoeckli H F, Rebstein P, BaUerini L (1990) On the Assessment of Microporosity in Active Carbons, a Comparison of Theoretical and Experimental-Data. Carbon 28 907-909... 

While a number of established characterization methods exist for mesopores and macropores, the assessment of microporosity is much less advanced, due to experimental difficulties and the lack of a suitable model for the interpretation of the isotherm data. Obtaining accurate experimental isotherms is hampered by the long equilibration times required at the low liquid nitrogen temperatures. In order to overcome this limitation the micropore structure evaluation can be based on isotherms of carbon dioxide or other vapors obtained at higher temperatures, provided that a suitable equilibrium model for the sorption of non spherical molecules is available. 

In Fig. 2 the PSD obtained by application of the t-plot method, using the Sooty Silica [25] and the nonporous carbon [24] as reference materials, are also shown. When the standard proposed by Selles-Perez [24] was used, a gradual increase of medium-sized micropores and mesopores was observed, while the volume of narrow micropores promptly decreased with the bum-off degree. As inferred from the application of this mediod, the PC76 sample did not presented narrow microporosity. This prediction is highly in disagreement with the PSD obtained by the DFT method. It seems that the SeUes-Poez reference material fails to predict the pore stmeture of microporous activated carbons, especially in the assessment of microporosity. 

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