Biomedical Engineering Reference
In-Depth Information
surfaces inside the bundles. In this model, the experimental value
of the specific surface area of single-wall nanotube samples agrees
with the theoretical value of the specific interbundle surfaces, which
is given by:
d
,
th
th
NT
S
S
(2.35)
b
ext
d
b
where
are the respective diameters of individual nanotubes
and bundles of single-wall nanotubes (see Figs. 2.1 and 2.2) and
d
and
d
NT
b
th
3
2
−1
S
is the theoretical value of the external surface
area of individual nanotubes [29]. Substituting the experimental
values
≈ 1.3 × 10
m
g
ext
th
exp
[72] in Eq. [35], we obtain the typical
value of the diameter of single-wall nanotube bundles
d
≈ 1.3 nm and
S
≈
S
NT
b
≈
3.4 nm.
The study of the sorption data [72] shows that a specific type of
physical adsorption occurs, involving a multilayer intercalation (or
condensation) of adsorbate in the interbundle regions of single-wall
nanotubes, where the interbundle surfaces are, apparently, decorated
with the adsorbate monolayer similar, both in composition and
structure, to the carbohydride adsorbate monolayer. In other words,
this specific physical adsorption in the interbundle nanoregions of
single-wall nanotubes may be initiated mainly by the formation of
a carbohydride adsorbate monolayer on the interbundle surfaces,
that can be ascribed to a chemisorption process (of type I and/or II,
Table 2.1).
The previous interpretation for the data [72] is confirmed, in
particular, by the proximity of the experimental value of isosteric
adsorption entropy ∆
d
b
ads
−1
−2
H
≈ −1.2 kJ mol
(H
) at (H
/C) ≈ 5 × 10
2
2
to the experimental values of the liquefaction enthalpy of gaseous
hydrogen ∆
[29, 31, 76], and to the results of the analysis and
comparison of the sorption data obtained in Refs. [72, 74, 77], which
we examine below.
The results reported in Fig. 2.16 [77] are particularly interesting.
Hydrogen sorption by single-wall nanotube samples (
H
liq
exp
S
≈ 285 ± 5
m
) have been
studied at 80 K and pressures up to 12 MPa. The 1996 Nobel Prize
winner in chemistry R. E. Smalley collaborated in this research, but
the results have never been reproduced by other researchers.
For the samples of activated carbon (Saran), a Henry-Langmuir
sorption isotherm appears under pressures up to approximately
7 MPa (curve 4 in Fig. 2.16), with a maximum saturation at
pressures ≥7 MPa, (H
2
g
−1
) and activated carbon (Saran) (
S
exp
≈
1600 m
2
g
−1
/C)
≈ 0.2, or at the maximum local adsorbate
2
m
