Biomedical Engineering Reference
In-Depth Information
4.4 
Conclusions
As a result of the experimental researches on the adsorption of
oxygen and nitrogen by three different adsorbents (fullerene,
astralene, and activated carbon) performed under various
conditions by the authors of this review, extensive data are now
available for studying the structural state of the investigated porous
materials, primarily fullerene and astralene. These data were used
to determine the characteristic values of several parameters to
describe the adsorption properties of porous materials, such as the
adsorption heat, specific surface area, pore size and volume and the
characteristic energy of adsorption for the three adsorbents with
respect to N
.
The obtained results agree with the data reported by other
authors rather closely. At the same time, measurements of the
oxygen and nitrogen sorption on fullerene at low temperatures
revealed a peculiar behavior of isobars not observed earlier for
fullerene. These data, however, are consistent with the anomalous
high absorption of CO
and O
2
2
at room temperature when compared
2
to the N
sorption at 77 K, as observed in Ref. [22]. Such
high adsorption values can be ascribed to the same phenomena
responsible for the behavior of isobars observed in this work for
temperature decreasing. This is the so-called molecular sieve effect
characteristic of a rather wide range of adsorbents and related to
the rearrangement of the crystalline structure of fullerene as the
temperature decreases. It is noteworthy that for carbon nanoclusters
(astralene) such effect is not observed due to the peculiarities of the
astralene structure, which is not subjected to any modification in a
wide range of temperature.
It is shown that the difference in the sorption capability between
fullerene and carbon nanoclusters (astralene) is primarily related
to the difference between their structures, as evidenced by X-
ray diffraction, and in particular to the differences in material
microporosity, specially remarkable for oxygen liquefaction in
these samples. It should be noted that, for a series of parameters,
astralene holds some intermediate position between fullerene C
and O
2
2
60
and activated carbon. On the other hand, the standard isotherms,
constructed for the adsorption of nitrogen and oxygen at 77 K on the
basis of the measured specific surface areas of the adsorbents, have
Search WWH ::




Custom Search