The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

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Gas Sensors Based on Conducting Polymers

We have used a nonlithographic deposition process to form single polymeric nanowire chemical sensors. Oriented polyaniline nanowires, with diameters on the order of 100 nm, were deposited on gold electrodes. The devices showed a rapid and reversible resistance change upon exposure to NH3 gas at concentrations as low as 0.5 ppm. The well-defined single-wire geometry allows for the characterization of the wire material and the device response. The response times of nanowire sensors with various diameters correspond to radius-dependent differences in the diffusion time of ammonia gas into the wires. The nanowire deposition process, utilizing a scanned microfabricated electrospinning source, presents a general method for interfacing polymeric nanowire devices with microfabricated structures.

Polymeric Nanowire Chemical Sensor

Polyaniline as a new sensitive layer for gas sensors

In this paper, we report conductometric sensors based on graphene/PANI nanocomposites, which were synthesized using chemical oxidative polymerization, for NH3 sensing. The experimental result reveals that the graphene/PANI sensor exhibits much higher sensitivity (ca. 5 times) than that of PANI, and shows approximate linearity over a wide range of concentrations from 1 to 6400 ppm. The detection limit of graphene/PANI sensor (ca. 1 ppm) is lower than that of PANI (ca. 10 ppm) for NH3. This shows that sensitivity of graphene/PANI sensor for NH3 detection is enhanced by the graphene added into PANI. The result is partially supported by experimental data that the NH3 adsorption of quartz crystal microbalance (QCM) coated graphene/PANI is larger than that of PANI. Meanwhile, the structure and morphology of the synthesized products are characterized by Fourier transform infrared spectroscopy (FTIR), brunauer emmett tellerand (BET), ultraviolet–visible spectroscopy (UV–vis), photoluminescence (PL), X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM), respectively.

Enhanced sensitivity of ammonia sensor using graphene/polyaniline nanocomposite

A polyaniline–titanium dioxide (PANI/TiO2) nanocomposite was prepared by an in-situ chemical oxidation polymerization approach in the presence of colloidal TiO2 at room temperature, and the PANI/TiO2 nanocomposite thin film was formed on a silicon substrate covered with interdigital electrodes to fabricate a gas sensor via the self-assembly method. The gas-responses of the PANI/TiO2 thin film to NH3 and CO toxic gases were examined. The results showed that the response, reproducibility and stability of the PANI/TiO2 thin film to NH3 were superior to CO gas. Compared with NH3 and CO gases, humidity had less effect on the resistance of the PANI/TiO2 thin film. It was also found that the difference between pure PANI and PANI/TiO2 thin films was not only in gas-sensing property but also in surface morphology.

M. Matsuguchi

Papers

Effect of NH3 gas on the electrical conductivity of polyaniline blend films