Biomedical Engineering Reference
In-Depth Information
electrons and the functional groups have only a secondary effect;
thus, the adsorption energies for the perpendicular configurations
are at least 150 meV smaller than parallel ones. The equilibrium
distances of the studied aromatic molecules are smaller than the
one for C
and are larger than the ones of the relevant functional
groups, with the exception of toluene. This circumstance indicates
that the distance is determined either by the
H
6
6
-stacking or by the
functional group that allows a closer interaction between the
molecule and the SWCNT.
Similarly to the other carbon nanostructures, doping of CNTs has
been proposed to undertake the weak binding of some molecular
species; Peng and Cho [80] have discovered that both B- and N-doped
CNTs experience a drastic change of conductivity when exposed to
carbon monoxide or water molecules; however CO molecules are
physisorbed onto N-doped CNT because no charge transfer occurs
while the binding energies and the equilibrium distances for the
B-doped case suggests that chemisorption takes place, as it will be
detailed in the following section.
p
8.5
Gas Chemisorption in Carbonaceous
Nanostructures
As mentioned in the previous sections, the adsorption scenario may
be sometimes quite complicated because physical and chemical
adsorption characters may coexist. In these cases, a detailed analysis
of the electronic structure is required to clarify the adsorption
processes involved. Such a deep description is beyond the scope of
the present chapter and thus in this section we limit our attention
only to those cases that can be unambiguously classified as chemical
adsorption phenomena between the species where bonding
events are predominant. Due to its importance, also in this case
we will treat the hydrogen case explicitly for some different carbon
nanostructured allotropes.
8.5.1
Hydrogen Chemisorption in Carbonaceous
Nanostructures
Generally speaking, hydrogen chemisorption in carbonaceous
nanostructures is not interesting for storage purposes because
