Biomedical Engineering Reference
In-Depth Information
As it is known [40, 41], also fullerenes possess the ability of
aggregation, and not only in solutions or suspensions, but also in a
solid powdered state.
As a consequence, for both astralene and fullerene, not only the
gases adsorption by these samples decreases, as it will be shown
below, but is reduced also the efficiency of singlet oxygen generation
during photodesorption from irradiated surface of the samples
[42].
The sorption capability of various samples was studied at
temperatures from 77 up to 323 K. Liquid nitrogen (77 K), a mixture
of acetone with solid carbon dioxide (205 K), and a refrigeration unit
(from 263 to 283 K) have been used to keep a constant temperature.
Temperatures higher than the room temperature were obtained
by a thermally stabilized heater. Thermal stabilization allowed
the temperature of samples to be held constant within ~1 K. We
used different amounts of adsorbent materials to check the effect
(reported in Ref. [22]) associated with the changes in properties of
adsorbents during sequential measurements. However, we have not
observed such an effect.
4.2
Experimental Results
The results of oxygen adsorption measurements on three adsorbent
samples are shown in Fig. 4.3. Oxygen adsorption isotherms on
fullerene C
, astralene, and activated carbon AG-3, measured at
~20°C, are shown in Fig. 4.3a. We see that the sorption capabilities
of fullerene and astralene are somewhat lower than those for AG-3.
However, note that the shape of the adsorption isotherm for these
adsorbents is slightly different from that of activated carbon. The
kinetics of oxygen sorption on fullerene and activated carbon at a
200 torr oxygen pressure is shown in Fig. 4.3b.
The features of the curves reported in Fig. 4.3 allow us to
suppose that, along with a surface adsorption, also a volumetric
sorption in micropores occurs in these experiments. According to
[19], the rate of the volumetric sorption is considerably slower. This
conclusion is confirmed also by the results of Ref. [43] where for
fullerene the dependence of oxygen sorption on the exposure time is
completely identical to the curve presented in Fig. 4.3b. The oxygen
adsorption isotherms on fullerene C
60
for the different adsorbent
temperatures are shown in Fig. 4.4. It is seen that in the temperature
60
