Effect of Ammonia Based Deprotonation on the variable range hopping conduction in Polypyrrole Nanotubes

Abstract

This paper reports the facial synthesis of polypyrrole (PPy) nanotubes by an anionic azo dye {sodium 4-[4-(dimethyl-amino)-phenyldiazo] phenylsulfonate} assisted chemical oxidation method and their deprotonation by liquid ammonia treatment. Scanning and transmission electron microscopy studies reveal the synthesis of PPy nanotubes of diameters ∼155 nm and their lengths are found to be about 2–3 μm. The deprotonation of PPy nanotubes by liquid as well as gaseous ammonia has been experimentally confirmed by Raman and FTIR studies. These spectroscopic techniques suggest the proton transfer based mechanism for deprotonation of the PPy nanotubes. The deprotonation of PPy nanotubes has also been confirmed through the electrical measurements carried out in the presence of ammonia gas at different ppm levels. Furthermore, the effect of deprotonation on the charge transport properties of PPy nanotubes has also been investigated. The temperature dependent conductivity measurements are performed on both the pristine as well as deprotonated (by liquid ammonia) PPy nanotubes in a wide range of temperature (77–400 K) and analyzed for different conduction mechanisms. However, both the samples are found to follow Mott's variable range hopping conduction process in three dimensions (3D-VRH) for the charge transport. The conduction properties of both the samples are further investigated in terms of Mott's 3D-VRH variables such as Mott's characteristic temperature, hopping distance, hopping energy, and density of states, etc.