Spectroscopic investigations of ammonia gas sensing mechanism in polypyrrole nanotubes/nanorods

In light of spectroscopic and electrical investigations, ammonia gas sensing mechanism in polypyrrole (PPy) nanotubes/nanorods has been discussed. For improvement in the gas sensing properties of PPy and its surface to volume ratio, nanotubes and nanorods have been synthesized by anionic dye and anionic surfactant directed chemical oxidation method. The gas sensing behavior of the prepared samples has been tested by measuring the change in electrical resistance of the samples in ammonia environment. Scanning electron microscopic investigations have confirmed the synthesis of PPy nanotubes having diameter ∼80–90 nm and length ∼1.5–2.0 μm and the PPy nanorods with diameter ∼150–200 nm and length ∼15–20 μm. The chemical analysis and the confirmation of synthesis of PPy were carried out by Fourier transform infrared and Raman spectroscopic techniques. Better sensitivity against ammonia has been observed in PPy nanorods. For the first time with the help of Raman spectroscopic investigations, the mechanism of gas sensing has been discussed in detail.