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2
−1
≈ 3000 m
) have been studied in Ref. [75]. The initial sections
of the Henry-Langmuir sorption isotherms become evident at
temperatures in the range 233-298 K and at pressures ranging from
about 0.1 to 11 MPa. The value of the sorption capacity for AKh-21 at
233 and 6 MPa reaches 0.9 wt%, with (H
g
s
−2
.
The deviation of the isotherm from linear behavior is about 30%,
corresponding to (H
/C) ≈ (H
/C
) ≈ 5.4 × 10
2
2
/C)
(H
/C
)
≈ 0.17, in accordance with
2
m
2
s
m
Eq. (2.34).
For multiwall nanotube samples, at 233 K and 10.3 MPa, the
sorption capacity reaches 0.27 wt% (H
−2
/C) ≈ 1.6 × 10
and (H
/
2
2
s
C
) ≈ 0.3, according to Eq. (2.33). The isotherm deviation from
linear behavior amounts to about 16%, corresponding to (H
exp
/C)
2
m
≈ 0.11 (Eq. (2.34)) and the anomalous value of the maximum local
adsorbate concentration (H
s
≈ 2 (Eq. (2.35)), which is several
times higher than the value for carbohydride.
Based on the Clausius-Clapeyron equation [68], the values of
isosteric enthalpy of hydrogen adsorption for multiwall nanotube
samples (∆H
/C
)
2
exp
m
ads
−1
)
for adsorbate concentrations ranging from 0.12 to 0.21 wt%, as well
as for activated carbon AKh-21 (∆H
) are in the range from −1.73 to −1.53 kJ mol
(H
2
ads
≈ −6.4 kJ mol
−1
(H
)) [75]. We
2
ads
note that the experimental value of ∆
for multiwall nanotubes is
relatively close to the liquefaction enthalpy of gaseous hydrogen at
20 K:∆
H
liq
−1
) [76].
The sorption characteristics for activated carbon [75] can be
interpreted using the monolayer chemisorption model (process I,
Table 2.1). The sorption characteristics of multiwall nanotube samples
[75], can be interpreted using the model of polylayer physical adsorption
(adsorbate condensation) discussed in the following section.
H
−0.9 kJ mol
(H
2
2.2.4.2 
Manifestation of Multilayer Physical Adsorption
Initiated by Monolayer Chemisorption in the
Single-Wall Nanotubes
Now we will discuss the data reported in Ref. [72] on the hydrogen
sorption by single-wall nanotubes (about 10 mg,
S
exp
≈ 500 m
2
g
−1
)
exp
2
−1
and graphite powder (about 100 mg,
) saturated with
hydrogen at fairly low pressures (from about 7 to 10
S
≈ 60 m
g
7
kPa, as in
Ref. [26]) and two temperatures, 295 K and 77 K (see Fig. 2.15a and
b). For the samples used in Ref. [72], in contrast to those studied in
Ref. [26], the adsorption isotherm exhibits a specific nonmonotonic
behavior at both temperatures, which can be interpreted as an
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