The assessment of surface areas in porous carbons by two model-independent techniques, the DR equation and DFT
✍ Scribed by T.A. Centeno; F. Stoeckli
- Publisher
- Elsevier Science
- Year
- 2010
- Tongue
- English
- Weight
- 300 KB
- Volume
- 48
- Category
- Article
- ISSN
- 0008-6223
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✦ Synopsis
The strong linear correlation observed between S BET and the micropore volume of 190 carbons with pore widths between 0.5 and 1.8 nm confirms the unreliable character of S BET , in spite of its frequent use. (It corresponds approximately to 2200-2300 m 2 per cm 3 of micropores, whatever their width). Alternative determinations of the surface area are therefore required. It is shown that two model-independent techniques (Kaneko's comparison plot for nitrogen and the enthalpies of immersion into aqueous solutions of phenol) and two model-dependent approaches (Dubinin's theory and DFT) lead to total surface areas which are in good agreement. Their average S av is probably a reliable assessment of the total surface area. It is often in disagreement with S BET , but a closer study of 42 well characterized microporous carbons, for which all four techniques are available, shows that the ratio S BET / S av increases linearly with the average pore width. This should be taken into consideration when surface-related properties (e.g., densities of chemical groups or adsorbed species, specific capacitances) are examined on the basis of a single determination and in particular on the BET technique.