Biomedical Engineering Reference
In-Depth Information
for clean single-wall
nanotube samples (about 90-95 wt%) with a mass of about 1 g [63],
Eq. (2.24) yields the value
Using the TPD data] on
β
-dependence of
T
m
-1,
which clearly points out the
diffusion nature of the process. Hence, using Eq. (2.22) and
K
≈ 0.2 s
0
D
from
0I
Table 2.1,
is about 1 mm, corresponding to the smallest linear size
of single-wall nanotube samples [63]. For
L
a similar value of about
1 mm is obtained when Eq. (2.25) is used [10].
In Ref. [63], the samples were saturated with hydrogen at 295 K
and at pressure in the range 1-9 MPa. An almost linear section of
the Henry-Langmuir adsorption isotherm appeared. The adsorbate
concentration at 9 MPa was nearly 0.3 wt% (
L
X
= H
/C ≈ 1.8 ×
2
-2
10
), with a relative deviation of the isotherm
X
from the linear
isotherm
*, of about 14%. To indirectly find
the maximum sorption capacity for single-wall nanotube samples
[63] corresponding to the Langmuir saturation
X
, given by (
X
*-
X
)/
X
X
= (H
/C)
, the
m
2
m
following formula can be used:
H
XX
*
,
(2.34)
2
X
m
*
C
X
x
m
which follows from Henry-Langmuir isotherm (14a), where (
X*- X
)
/
X*
is the relative deviation of the experimental sorption isotherm
[63] from the Henry isotherm, and
is the adsorbate concentration
corresponding to the Henry isotherm, for a given experimental value
of
X*
corresponding to the Langmuir isotherm.
Thus, for the single-wall nanotube samples measured in Ref.
[63], we obtain the maximum adsorbate concentration
X
≈ 0.13,
corresponding to the theoretical value of the total specific surface
area of single-wall nanotubes,
X
m
th
, (calculated using Eq. [33]), i.e.,
an average of the concentration over the whole (both external and
internal) specific surface area of the adsorbate (according to the
sorption monolayer model).
When the adsorbate is located on definite sections of the sorption
monolayer corresponding to the experimental value of the specific
surface area
S
tot
, the maximum local concentration of the adsorbate
can be estimated, as an order of magnitude, by the following formula
(from Eqs. (2.33) and (2.34)) :
The results reported in Ref. [63] for single-wall nanotubes
are described fairly well by the adsorption isotherm for a type-I
process (Eq. (14a)), with the following characteristics: ∆
S
exp
H
ads
≈ −8.5
-1
ads
kJ mol
(H
) ≈ ∆
H
,
∆
S
/
R
≈
∆
S
/
R
≈ -21, and
X
= (H
/C)
2
(13)I
(13)I
m
2
m
