Determination of the specific surface area and the pore size of microporous carbons from adsorption potential distributions
- Kent State Univ., OH (United States). Dept. of Chemistry
- Corning, Inc., NY (United States)
Porous structures of synthetic active carbons were characterized using nitrogen adsorption at 77 K over a wide range of relative pressures (10{sup {minus}7}-0.995), and it was shown that the analysis of adsorption potential distributions (APDs) in many cases allows for estimation of the specific surface area and the average micropore size. The APDs for most of the samples had two peaks, which can be related to the monolayer formation on the micropore surface and to the secondary micropore filling. The minimum between these two peaks was identified as a point of completion of the monolayer, allowing for evaluation of the specific surface area in a good agreement with the calculations made using the advanced DFT Plus software. Assuming the slitlike pore geometry, the obtained specific surface areas were used to calculate average micropore sizes for the synthetic active carbons as well as for commercial high-surface-area porous carbons. The amounts adsorbed per unit surface area (normalized adsorption curves) were calculated for these samples and showed a systematic change with the average micropore size. As the latter increased, the normalized adsorption at low pressures (below ca. 10{sup {minus}3}) gradually decreased and for samples with larger micropores it became more and more similar to the normalized adsorption on a macroporous nongraphitized carbon. In addition, a gradual development of the secondary micropore filling was observed. The position of peaks on APDs was related to the average micropore size providing another simple method of micropore size estimation. The observed changes in the low-pressure adsorption behavior correlate well with those predicted by computer simulations and DFT calculations, but the experimentally observed monolayer-formation and secondary-micropore-filling transitions were smoothed, which can be attributed to the surface and pore-size heterogeneity.
- OSTI ID:
- 328226
- Journal Information:
- Langmuir, Vol. 15, Issue 4; Other Information: PBD: 16 Feb 1999
- Country of Publication:
- United States
- Language:
- English
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