Biomedical Engineering Reference
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≈ 0.13 (rather than
X
≈ 0.5, as assumed in examining the data in
m
Ref. [26]).
The above-mentioned arguments show that for single-wall [63]
and multiwall [62] nanotube samples, a physical-like chemisorption
process of type I occurs. The results of this analysis and of the
comparison of TPD and sorption data for single-wall nanotubes,
single-wall nanohorns, and multiwall nanotubes are listed in
Table 2.3.
A similar conclusion is found examining the experimental data
in Ref. [64] on sorption isotherms for samples of clean single-wall
nanotubes and activated carbon. The samples were saturated with
hydrogen at 273-323 K and pressures up to 10.7 MPa (Figs. 2.11 and
2.12) and fabricated by a highly accurate volumetric method using
a pressure-drop chamber. For single-wall carbon nanotubes, the
authors of Ref. [64] used the Clausius-Clapeyron equation to find
the experimental value of isosteric adsorption enthalpy ∆
ads
H
≈ −8.5
−1
± 1 kJ mol
(H
) (see the inset in Fig. 2.11), which is close to the
2
value of ∆
for chemisorption process I.
Using Eq. (2.34) to process the three adsorption isotherms at 323,
298, and 273 K in Fig. 2.11, related to single-wall nanotube samples
with specific surface area
H
(13)I
exp
2
-1
S
≈ 609 m
g
, the values
X
= (H
/C)
≈
m
2
m
X
s
0.045-0.055 are obtained. Applying Eq. (2.35), the values
= (H
/
m
2
s
C
≈ 0.19-0.24 are achieved. The last ones are close, as order of
magnitude, to the carbohydride values listed in Table 2.1.
Using the experimental values of ∆
)
exp
m
ads
H
and
X
/
X
,
and applying
m
ads
Eqs. (2.14) and (2.15) for process I, the value ∆
S
/
R
≈
−21.3
≈
∆
S
/
R
is obtained.
(13)I
Table 2.3
Sorption data for different carbon nanostructures
Single-wall nanotubes
Single-wall
nanotubes
[31]
Multiwall
nanotubes
(62)
Parameter
[63]
[64], Fig.
11
des
,
kJ
-1
(H
E
20 (
,
Table 1)
Single-wall
nanohorns
(19), (24)
≈
Q
20
Equations
(19), (24)
a
I
—
—
)
2
K
,
s
-1
10
Equations
(19), (24)
∼
0.2
Equations
(19), (24)
0
—
—
