Synthesis and characterization of methanesulfonic acid doped poly(2-chloroaniline), study of its physical properties and ammonia gas sensing application

The poly(2-chloroaniline) was prepared by in situ chemical oxidative polymerization method using ammonium thiosulphate as an oxidant and methanesulfonic acid as a dopant. The optical absorption spectra showed bands for π-π* transition of the benzenoid ring at 265 nm and at 350 nm for n-π* transition of the quinonoid ring. The broad band appeared around 550 nm was due to transition of electrons from the valance band to the conduction band, this also confirmed the good electrical conductivity of the polymer. The X-ray diffraction pattern showed characteristic diffraction peak at 2θ = 26° confirming a emeraldine salt form of the poly(2-chloroaniline). The electrical conductivity of the polymer measured by the two probe method at room temperature was 2.21×10^?3 S/cm, which was found to be thermally activated. The linear increase in conductivity with increase in the temperature suggested the electron hopping mechanism. The methanesulfonic acid doped poly(2-chloroaniline) presents a linear dependency of its electrical resistance with an increase in ammonia gas concentration (1 ppm to 300 ppm) and creates a promising sensing material for ammonia gas sensing applications.