Biomedical Engineering Reference
In-Depth Information
Pt surfaces are known to adsorb small gaseous molecules
reversibly and therefore Pt doping of SWCNT has been proposed to
increase the uptake [26, 115]. DFT calculations of molecular hydrogen
on Pt-doped armchair nanotube have shown that chemisorption is
accompanied by an oxidative addition to Pt involving the 5
orbital.
However, Pt-Pt coupling is stronger than Pt-SWCNT interaction and
thus Pt clusters may form on the CNT sidewall [26].
Pd decoration of SWCNT behaves similarly [114] with a storage
capacity of about 3 wt.%. The most stable configuration exhibits both
the physical and chemical adsorption characters with five hydrogen
molecules adsorbed onto two adjacent Pd atoms on the CNT external
sidewall through a slight hybridization between the H
d
s
-orbital and
2
the Pd
d
-orbitals.
8.5.2
Gas Chemisorption in Carbon Nanostructures
for Sensoring
As mentioned in the introduction, in the recent years gas chemical
adsorption in carbon nanostructures, mainly graphene, CNTs and
fullerenes, has been studied with the principal aim to investigate
the possible application of such structures for gas sensoring. Of
course, the computational techniques required fall into the quantum
chemistry techniques such as the DFT total energy calculations and
similar. Due to the amount of the literature found, we have focused
our attention on nanostructured graphene and CNTs.
8.5.2.1
Graphene-Based Nanostructures
Graphene charge carrier concentration can be strongly modified
by gas chemisorption and therefore a considerable effort has been
devoted to study the electronic and magnetic properties of GNRs
and their modifications by edge functionalization or substitutional
doping. Dangling bonds (DBs) at the GNRs edges enhance the
covalent bonding of chemical species thus playing a critical role in
the feasibility of using such carbon based nanostructures as gas
sensors. Semiconducting AGNRs are preferred over ZGNRs since the
adsorption of gas molecules is expected to induce little modifications
on the electronic properties of metallic ZGNRs.
Adsorption of many gas molecules (CO, NO, NO
, O
, CO
,
2
2
2
and NH
) have been studied by spin-polarized DFT total energy
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