Fig. 3. FTIR analysis. (a) Polyaniline film and (b) ammonia exposed polyaniline film.
3.4. XRD analysis
The X-ray diffraction pattern of PANI as shown in Fig. 4 exhibited a highly disordered arrangement [41]. The pattern affirmed the amorphous nature of deposited PANI. A broad wide scattering around 2θ = 26◦ was evident which was probably due to the perpendicular periodicity of the X-ray beam to the polymer chain [42].
Fig. 4. XRD graph of polyaniline emeraldine salt.
3.5. Electrical impedance spectroscopy
The shape of the Nyquist plot obtained might be modeled by a typical doubly superimposed Randle’s circuit depicted in Fig. 5(a). The Nyquist plot yielded two semi circles entailing two halves of the frequency spectrum. An overlay of the Nyquist plots obtained
experimentally is given in Fig. 5(b).
Fig. 5. (a) Simple representative electrical circuit to model the experimental impedance data of the PANI ammonia sensor. R1 represents the contact resistance, R2 and R3 are the charge transfer resistances operationally effective at high and low frequencies respectively. The capacitances C1 and C2 are respectively important at high and low frequencies. (b) Nyquist plot of 5 ppm ammonia concentration.