Biomedical Engineering Reference
In-Depth Information
seen from the graphs that different characteristic linear curves have
been found toward toluene and m-xylene with a slope of 0.9 and 1.8
Hz/ppm, respectively. Thus, the sensitivity for m-xylene is higher
than that of toluene.
Furthermore, the effect of the number of SWCNT LB monolayers
on the QCM sensor response is also investigated. To this aim, sensors
coated by a different number of 4 and 10 SWCNTs monolayers have
been exposed simultaneously to m-xylene and toluene vapors, at
room temperature. It can be seen that, a higher number of SWCNTs
monolayers leads to higher sensitivities caused by a larger gas
adsorption capability of the thicker layers.
[295] demonstrated a QCM device coated by a HiPco
SWCNT layer for examining the gas adsorption of O
Wei
et al.
, and
Ar onto SWCNT surface. The change in frequency was found to
be proportional to the amount of adsorption in the QCM device
according to Sauerbrey theory, i.e., the changes in frequency are
expressed as adsorption isotherms. The binding energies of these
gases on the SWCNT samples exceeded those obtained for the same
adsorbents on planar graphite, by approximately 41-52%.
, N
2
2
. [191, 194] fabricated a low-humidity sensor made
of a QCM coated with MWCNT/Nafion composite material films.
The microstructure of these MWCNT/Nafion composite material
films showed a strong interaction between MWCNTs and Nafion.
The MWCNT/Nafion composite material films coated on the gold
electrode of QCM showed excellent sensitivity (e.g., 3.56 Hz/ppmv
at 23.4 ppmv), linearity (
Su
et al
2
= 0.9604) and short response time
(23 s at 83.5 ppmv). The water vapor molecules adsorbed onto the
MWCNT/Nafion films showed higher frequency shift than Nafion
and SWCNT/Nafion films. The adsorption dynamic analysis based
on association constant was used to elucidate the effect of adding
SWCNTs and MWCNTs into Nafion on the increased sensitivity of the
low humidity sensing in the range lower than 1%.
R
. [296] investigated the low humidity
sensing performance of raw MWCNTs, oxidized MWCNTs (MWCNT-
COOH) and Pd-modified MWCNT-COOH (Pd-MWCNT-COOH) thin
films by using a QCM. Water vapor molecules adsorbed onto the
Pd-MWCNT-COOH thin film had a larger frequency shift than raw
MWCNTs and MWCNT-COOH thin films. Adsorption dynamic analysis
and molecular mechanics calculations were applied to elucidate how
surface modification and functionalization of MWCNTs increased the
sensitivity to low humidity (0.2-1%).
The same group of Su
et al
