Single-Walled Carbon Nanotube–Poly(porphyrin)
Hybrid for Volatile Organic Compounds Detection
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Abstract
Porphyrins due to their unique and
interesting physicochemical
properties have been widely investigated as functional materials for
chemical sensor fabrication. However, their poor conductivity is a
major limitation toward the realization of porphyrin-based field-effect
transistor/chemiresistor sensor. The issue of conductivity can be
overcome by exploiting the excellent electrical property of single-walled
carbon nanotubes (SWNTs) to make a SWNTs-based hybrid device in which
SWNTs would act as a transducer and porphyrin as a sensory layer.
The present attempt was to fabricate a SWNTs–poly(tetraphenylporphyrin)
hybrid through electrochemical route and to evaluate its potential
as a low-power chemiresistor sensor for sensing acetone vapor as a
model for volatile organic compounds. Functionalization of SWNTs with
porphyrin polymer by the electrochemical method resulted in a fuller
coverage of SWNTs surface compared to a partial coverage by adsorption
and thereby higher sensitivity. SWNTs were coated with poly(tetraphenylporphyrin)
of different thickness by applying different charge density to optimize
sensing performance. Differences in sensing performance were noticed
for hybrids fabricated at varying charge densities, and the optimum
sensing response was found at 19.65 mC/cm<sup>2</sup>. The hybrid
exhibited a wide dynamic range for acetone vapor sensing from 50 to
∼230 000 ppm with a limit of detection of 9 ppm. The
field-effect transistor studies showed a negative threshold voltage
shift and almost constant transconductance when exposed to air/analyte,
indicating electrostatic gating dominated sensing mechanism. Further,
the results confirmed a good stability of the device over a period
of 180 days. The long-term device stability along with the sensing
capability at low analyte concentration with a wide dynamic range
and easily scalable fabrication technique signify the potential of
SWNT–poly(porphyrin) hybrid for volatile organic compound sensing
applications