Biomedical Engineering Reference
In-Depth Information
s*
*
maximum local concentration (H
≈ 0.5, corresponding to the
carbohydride value for process I. In such a framework, the data in
Fig. 2.14 [73] can be considered coincident with the ones in Fig. 2.12
[64].
With this interpretation, the sorption-active regions of the
surface of clean single-wall nanotubes [73] represent only about
16% of the theoretical value
/C
)
exp
2
m
th
[9, 29] of the total surface area of the
tubes. A similar situation occurs with the clean single-wall nanotube
samples in Ref. [31], where, as mentioned above, the percentage of
surface sorption-active sections does not exceed 12-39% of
S
tot
th
.
The behavior of the initial untreated nanotubes described in
Ref. [73] is in full agreement with the Henry-Langmuir adsorption
isotherm (see Fig. 2.13) with the maximum saturation (H
S
tot
/C)
≈ 8.7
2
m
−3
× 10
(0.145 wt%) at approximately 1.4 MPa, which corresponds
to the carbohydride value of the maximum local concentration
(H
s
≈ 0.5 (from Eq. [33]). The desorption isotherm for
untreated single-wall nanotubes was characterized by a slight
increase in the adsorbate content (from 0.145 to 0.152 wt%) as the
pressure decreases from 2 to about 1 MPa, a plateau in the adsorbent
content as the pressure decreases from about 1 to 0.5 MPa, and a
slight decrease in the adsorbent content (down to 0.125 wt%) as the
pressure lowers from about 0.5 MPa to zero.
/C
)
exp
2
m
Figure 2.13
Isotherms of sorption (1 and 2) and desorption (3 and 4)
of hydrogen at room temperature by the initially untreated
(1 and 3) and clean (2 and 4) single-wall nanotubes [73].
