An in situ synthesis of polyaniline/reduced graphene oxide nanocomposite flexible thin film on PET for the room temperature detection of trace level ammonia at ppb level

Ammonia being a major environmental pollutant, the regulation and its specific detection are tremendously important. To meet the urgency, the present article brings out a cost-effective, easy handling and enduring material of reduced graphene oxide (rGO)-doped polyaniline (PANI). Attempting an in situ chemical oxidation technique, thin films of this material were prepared on polyethylene terephthalate substrates at different doping percentages of rGO, varying between 0 and 10%. Furthermore, during the synthesis, various amount of hydrochloric acid (HCl) was dissolved within the precursor solution to achieve different acid molar concentration ranging between 0.1 (M) and 2 (M). Structural and compositional analysis of the materials was performed with X-ray diffraction. Three different spectroscopic studies, Fourier transform infrared (FTIR), Raman and ultraviolet–visible (UV–VIS) spectroscopy, were further carried out to analyse the chemical bond, vibrational modes and band gap, respectively. In addition, the surface morphology of the thin films was examined with field emission scanning electron microscopy (FESEM). To know the accurate size of the PANI and rGO, high-resolution transmission electron microscopy (HRTEM) was conducted. The study of ammonia (NH3) sensing in the domain of 50 ppb to 80 ppm exhibits lucrative sensitivity (~ 486% @ 80 ppm and 33% @ 50 ppb) at room temperature (25 °C), outstanding repeatability in the response curves, well-fitted response curve with the power-law (P ~ 0.71), much faster response/recovery times (tres/trec = 2.1 s/57.1 s @ 80 ppm and 3.7 s/112.9 s @ 50 ppb) and incomparably high selectivity towards NH3. The rGO doping variation, and HCl molarity variation, yield that all of the aforementioned supremacy data have been exhibited by 1% PANI-rGO sample synthesised in 1(M) HCl concentration. The frequency dependence of the sample impedance was studied using impedance spectroscopy in the wide frequency range. Density functional theory calculations were also performed to understand the charge transfer mechanism, adsorption strength, and recovery time for NH3 adsorbed rGO, PANI and rGO-PANI heterostructure. The significant charge transfer and formation of the interfacial electric field explained the importance of the rGO-PANI interface in NH3 sensing.