Biomedical Engineering Reference
In-Depth Information
Figure 2.12
Dependence of the sorption capacity of samples of the initial
(Δ) and ground (cut) (
) single-wall nanotube samples and
carbon (
) at 10.7 MPa and 298 K on their specific surface
area, determined by N
-BET method [64].
2
The data from Ref. [64], presented in Fig. 2.12, indicate that
only a fraction, about one-half, of the specific surface area
exp
of the
single-wall nanotube samples related to Fig. 2.11 is sorption-active;
this suggests the possibility of higher values for the maximum
adsorbate concentration,
S
s
s
≈ 0.4-0.5. As noted in Ref.
[64], the experimental values of the adsorbate concentration could
be systematically under evaluated (by up to about 20%) because the
effect of helium adsorption has been ignored, making possible even
higher values of
X
= (H
/C
)
m
exp
2
m
s
.
Similar processing, via Eqs. (2.34) and (2.35), of the adsorption
isotherm (298 K, up to 13 MPa
X
m
⋅
-2
, X
≈ 4.2
10
) for activated-carbon
th
s
exp
2
-1
samples (
≈ 0.12,
which is close, as order of magnitude, to the value for carbohydride:
∆
S
≈ 3135 m
g
≥
S
) yields the value
X
≈
X
m
tot
m
).
Thus, it can be assumed that a physical-like chemisorption
process of type I may occur in the single-wall nanotube samples
used in Ref. [64]. We note that the researchers provide an extended
definition of physical sorption without examining the nature and
energies of the interaction, while stressing the nondissociative nature
and the relative fast kinetics of the sorption process. Obviously, a
chemisorption process of type I formally satisfies such definition.
The isotherms of hydrogen adsorption by clean samples
(95 wt%) of single-wall carbon nanotubes with horn-like ends
(nanohorn), containing a relatively low amount (≤ 5 wt%) of metallic
H
ads
≈ −4 kJ mol
−1
(H
2
