Biomedical Engineering Reference
In-Depth Information
tested methanol concentration range, as reported for the three
calibration curves in Fig. 9.23b with the several nanocomposites.
The chemical patterns of the SAW sensitivity to alcohols measured
by using three LB 75 wt.% nanocomposite films with different fillers
of raw (AG-SWCNTs), oxidized (OX-SWCNTs) and oxidized-plus-
acid-treated (OA-SWCNTs) nanotubes are reported in Fig. 9.23c.
The comparison indicates that the purification process utilized for
the HiPco SWCNTs tailors the alcohol sensitivity of the SAW sensors
based on the LB nanocomposite films, with the highest sensitivity
achieved with a filler of oxidized nanotubes for all tested alcohols.
This is attributed to enhanced acoustoelectric effect.
. [61] demonstrated that HPNTs containing Fe particles
were purified by a one-step process with HCl washing (D-method)
and a two-step process with HCl washing after air oxidation (GD-
method). The TGA analysis showed a decreased Fe content after
purification. In addition, XPS results provided evidence that oxygen-
based functional groups were introduced to the nanotube surface by
both purification methods. The purification processes also altered
the N
Yang
et al
adsorption isotherms with accompanied development of the
microporosity in the nanotubes. Thus, purification considerably
affects the surface chemistry and pore structures of the HPNTs
aggregates. The effects of purification on the adsorption properties
of the HiPco SWCNTs aggregates were considered related toward
methanol (CH
2
OH) vapors at 303 K. The
purification greatly enhanced the adsorptivity for both alcoholic
vapors considered under a low relative pressure. This was associated
to the enhanced microporosity and the oxygen-based functional
groups introduced on the surface of the treated CNTs.
Although these results were considered to demonstrate that
the purification enhances the gas adsorption in the CNTs, these
protocols can be applied to the CNTs to increase their gas adsorption
capability, and consequently their improved gas sensing properties
in terms of higher gas sensitivity and faster response time.
OH) and ethanol (C
H
3
2
5
9.4.4
Functionalized CNTs
The functionalization of the CNTs is a powerful strategy to improve
gas sensitivity and fabricate selective nanomaterials. Function-
alizing the surface of these nanostructures offers another route
for expanding their chemical sensing capability. In fact, the charge
