Biomedical Engineering Reference
In-Depth Information
structures that, at least in principle, are suitable for gas storage
[37, 103, 119].
By doping fullerenes, either via substitutional impurities or
via surface decoration, molecular hydrogen adsorption can be
improved, and many examples can be found involving alkali metals
[22, 52, 97, 118] and transition metals (TMs) [89, 117, 122]. Thanks
to van der Waals interactions, CNTs [47, 86] can be arranged in
arrays or bundles where gas molecules can be stored at different
adsorption sites both inside and outside the CNTs. Hydrogen storage
has been intensively studied with different approaches [4, 63, 69,
93, 107] but, from the recent literature, it emerges that H
molecules
are weakly bound. Similarly to fullerenes, CNT doping with metal
species can affect the adsorption [114, 115] making them suitable
for gas sensoring [1, 6, 16, 121]. B- or N-doped CNTs have revealed
nice adsorption properties for H
2
O and CO molecules [80] while
zig-zag SWCNTs, doped with various TMs (from Ti to Zn), have been
studied for the detection of N
2
S [35]. Pt-
doped armchair nanotubes have been employed in the detection
of CO, NO, N
, O
, H
O, CO, NH
, and H
2
2
2
3
2
[115] and armchair SWCNTs and their bundles have
been studied in connection with various gas molecules (NO
2
, O
,
2
2
NH
O) [121]. However, one of the major difficulties
for the usage of metal doped SWCNTs in sensoring devices is that
their transport properties are weakly dependent on the amount of
the adsorbed molecules which makes difficult the detection and the
identification of the various species [36].
Among the other carbon nanostructure, single-walled carbon
nanohorns (SWCNHs) have been suggested for adsorption and have
been studied both experimentally and theoretically [30].
, N
, CO
, and H
3
2
2
2
8.3
Theoretical Methods
The interpretations and the predictions of the experimental results
concerning gas adsorption properties of carbon nanostructures
are usually addressed by means of atomistic simulation, quantum
chemistry techniques, and, less frequently, by theoretical models
derived from the continuum theory of fluids.
Of course, chemisorption, bond breaking, and bonding events are
typically addressed by quantum chemistry techniques or electronic
structure and total energy calculations; therefore, most of the
literature on carbon nanostructures as gas sensors, which requires
