In the present investigation, we have synthesized a polypyrrole films by chemical polymerization technique for the development of ammonia sensor. The polypyrrole films were synthesized in an aqueous acidic medium on glass substrate with mild oxidation of ferric chloride at temperature 29-C. The concentrations (molar) of monomer (pyrrole), oxidant (ferric chloride), and dopant (polyvinyl sulfonate) have been optimized for the uniform and porous surface morphology of the synthesized polypyrrole film. The synthesized films were characterized by scanning electron microscopy, ultraviolet-visible, and Fourier transforms infrared spectroscopy. Ammonia gas sensing behavior of polypyrrole films was studied by using indigenously developed gas sensing chamber. The synthesized polypyrrole film with optimized process parameters shows excellent and reproducible response to low concentration (100 ppm) of ammonia gas.

Single-walled carbon nanotubes have been noncovalently functionalized with metalloporphyrins. Iron tetraphenyl porphyrin and cobalt tetraphenyl porphyrin were independently employed to functionalize aligned nanotubes network that formed the channel material for chemical field effect transistor-based sensors. The primary aim of the study was to achieve discrimination among structurally similar aromatic hydrocarbons, benzene, toluene, and xylene, and derive possible role of the central metal ions present in the metalloporphyrins in defining sensor selectivity. Current−voltage and field effect transistor measurements have confirmed formation of the efficient charge transfer complex during functionalization. The sensors were validated in respect to the analyte atmosphere within a concentration window of 500 ppb to 10 ppm. A clear affinity of the sensors toward toluene was recorded; however, the iron tetraphenyl porphyrin functionalized sensors exhibited a clear response (change in normalized resistance = 0.728) at lowest concentration validated, approximately 30% sensitivity (500 ppb to 10 ppm concentration) and excellent linearity (R 2 =0.94) with figures that are significantly better than cobalt tetraphenyl porphyrin-based devices. Observed behavior of the sensors have been rationalized in terms of vacant d orbitals of the central metal ions of metalloporphyrins and the side substituents present in the structure of the hydrocarbons validated.

Electrochemically controllable functionalization of single-walled carbon nanotubes (SWNTs) with poly(N-methyl pyrrole) (P[NMP]) is demonstrated for room temperature gas sensing applications. Comparative investigations reveal that the loading content of the functionalization entity has prominent effects on the sensing characteristics of SWNTs. The optimized sensing backbone (P[NMP]-functionalized SWNTs with 5 µC deposited charge) exhibited a lower detection limit of 10 ppb and excellent linearity for a detection window of 10 ppb–01 ppm concentration of NH3. The typical response and recovery time of the optimized sensor is on the order of minutes. Finally, a performance comparison of the P[NMP]-functionalized SWNT sensing backbones with the pristine P[NMP] nanowire sensor ensured the well-defined role of SWNTs in the functionalized structure. The proposed sensing mechanism suggests that the synthesis parameters can be manoeuvered for the highest operational efficiency of the sensors.

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