Biomedical Engineering Reference
In-Depth Information
the formation of covalent C-H bonds, i.e., to chemisorption. Process
γ
, inactive in the IR spectrum but responsible for the anomalous
change of the diffraction pattern of the multilayer GNF structure
subjected to hydrogen saturation (see Figs. 2.18 and 2.19), relates
results reported in Ref. [94] to the molecular hydrogen intercalated
between the graphene layers in the bulk of nanofiber.
The concept of a molecular hydrogen building-up between the
graphene layers is recalled here; this concept is formulated in Refs.
[14, 96], a study of the mechanical synthesis of hydrogen with graphite,
upon grinding by ball mills, and in Ref. [52], where the interaction of
atomic hydrogen and graphite has been examined.
The results of the critical and constructive data analysis,
processing, and interpretation performed in Refs. [14, 52, 96] and
presented in Refs. [10, 97], is not taken into account in Ref. [94]. The
authors believe to be able to fabricate thermally stable compounds
containing up to 6.8 wt% of hydrogen, the bigger fraction of which
is in a new state characterized by the absence of vibrational C-H
modes in the IR spectra.
Overall, we believe that a better interpretation of this state,
corresponding to process
γ
, and a more detailed description
of process
, should be possible, on the basis of the following
experimental facts:
β
(1) The appearance of a Sievert dissociation sorption isotherm for
single-wall nanotube samples studied in Refs. [94, 95], which
points to the atomic rather than molecular state of the larger
fraction the adsorbate (
γ
);
(2) The desorption temperatures for process
γ
being higher
than those for process
β
, which points to a higher desorption
activation energy (
Q
γ
> Q
β
);
(3) The absence of vibrational C-H modes in the IR spectra (at
500-5000 cm
, Fig. 2.19) for process
γ
, in contrast to process
−1
, which obviously points to a significant difference in the
mechanisms of these processes;
(4) The anomalous change in the diffraction pattern (see Fig. 2.18)
of the multilayer structure of GNF for process
β
, caused by an
increase (up to 40%) in the interplanar spacing between the
graphene layers in the GNF, which indicates that the adsorbed
hydrogen (
γ
γ
) is localized between the graphene layers;
(5) The presence in the single-wall nanotube samples studied in
Ref. [94] of up to 40% of graphite multilayer nanoparticles
