Electrochemical sensors based on carbon nanotubes - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 492

0.011

(c)

0.01

(b)

(a)

0.009

0.008

0.007

0.006

3500 3400 3300 3200 3100 3000 2900 2800

Frequency (cm 1 )

FIGURE 15.26 FTIR spectra of SWNT after exposure to NH 3 microwave plasma: (a) SWNT on CaF 2
substrate after heating; (b) after 20 min of plasma exposure; (c) after 40 min of exposure. (Reprinted with
permission from [140]. Copyright (2004) American Chemical Society.)

PPy/CNT composite fi lm using both FTIR and Raman spectroscopy. The fi lms were
obtained by repeatedly cycling the potential in the range of 0.8 V in an aque-

ous solution of 0.1 mol L 1 SDS, 25 mmol L 1 pyrrole, and 0.17 g L 1 single-walled
carbon nanotubes. The FTIR spectrum shows characteristic absorption bands of PPy
and doped SDS but no corresponding band from CNT. For example, the strong peaks at
1549 and 1469 cm 1 are due to the antisymmetric and symmetric ring-stretching modes
of the PPy, respectively. The peak at 1176 cm 1 indicates the doping state of polypyr-
role, and the peaks at 1045 cm 1 and 1315 cm 1 are attributed to C ß H deformation
vibrations and C ß N stretching vibrations of the PPy, respectively. Two very strong
peaks around 2914 cm 1 and 2846 cm 1 were attributed to the stretching vibration mode
of methylene, indicating that surfactant SDS had been doped into the chains of PPy.
FTIR is also an effective way to assess the orientation or alignment of CNTs since
the absorption is much stronger when the electric fi eld of the incident light wave is
parallel to the axis of aligned CNTs. The anisotropic feature has been found in SWNT-
PAN composite [164]. The infrared spectra of PAN fi bers for the two polarization
directions (parallel and perpendicular) are comparable, while the composite fi bers
show signifi cant differences in the two polarization directions.
Zengin et al. [41] characterized a polyaniline (PANI)/MWNT composite. The FTIR
spectra of the composite fi lm show benzoid and quinoid ring vibrations at 1500 cm 1
and 1600 cm 1 , respectively, which indicate the presence of emeraldine salt (ES) of
polyaniline. A weak broad band near 3400 cm 1 is assigned to the N ß H stretching
mode. The strong band at 1150 cm 1 is characteristic of PANI conductivity. The FTIR
spectrum of PANI/MWNT composite in the ES form exhibits several clear differences
from the spectrum of neat ES PANI: (1) the composite spectrum shows an inverse

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