Biomedical Engineering Reference
In-Depth Information
At the same time, the isosteric adsorption enthalpy at (H
/C) ≈
2
−2
5 × 10
for single-wall nanotube samples and for graphite samples
amounted to only ∆
ads
−1
), which considerably
differs (by almost an order of magnitude) from the ∆
H
≈ −1.2 kJ mol
(H
2
H
value of
(13)I
the chemisorption process I.
The sorption capacity of single-wall nanotube and graphite
samples used in Ref. [72] at 295 K and 10
7
kPa, calculated for
2
−1
S
≈ 1000 m
g
, is given by approximately 1.9 and 1.3 wt% per
1000 m
, respectively. These values are relatively close to the
similar characteristic value 1.5 ± 0.2 wt% per 1000 m
2
g
−1
2
−1
obtained
in Ref. [29] for electrochemically hydrogen-saturated single-wall
nanotube and graphite samples with the specific surface area ranging
from 50 to 1200 m
g
2
−1
(experimental values), which is compatible
with the surface nature (localization) of the sorption processes
considered.
The authors of Ref. [72] noted that for single-wall and graphite
samples at 77 K, the indirect values (following from their sorption
data) of the local adsorbate surface concentrations cannot be
explained by the known mechanisms of physical monolayer sorption.
They substantially exceed the maximum adsorbate concentrations
corresponding to the adsorbate monolayer structure commensurate
with the graphene structure [(H
g
s
) ≈ 0.17] and with the close-
packed adsorbate monolayer structure, not related to the graphene
structure [(H
/C
2
) ≈ 0.25].
It is worth noticing that the hydrogen adsorption isotherms of
the single-wall nanotube samples studied in Ref. [72] do not reach
a saturation plateau (see Fig. 2.15), i.e., there is no tendency toward
Langmuir saturation even at 77 K (in contrast to the case of single-
wall nanotube samples in Ref. [26]).
Another important property is that the maximum (carbohydride)
values of the adsorbate concentration manifest themselves only
when local concentrations are considered, i.e., recalculating the
experimental values of H
/C
s
2
/C using Eqn. [33] for local values of H
/
2
2
s
C
.
exp
This approach is used under the assumption that the entire ad-
sorbate is localized on the experimentally determined specific sur-
face area
of single-wall nanotubes. The physical interpretation
can be that the external surfaces of single-wall nanotube bundles,
or the interbundle surfaces, play a dominant role in sorption (for
kinetic and/or other reasons), compared with the role of nanotube
S
exp
