Flexible and highly sensitive polyaniline-based (PAni) ammonia (NH₃) gas sensors were developed through in-situ chemical oxidative polymerization of aniline on a polyethylene terephthalate substrate at three different temperatures, viz. 35 °C, 0 °C and −5 °C. In the initial stage, they were characterized with respect to their structural, morphological, and compositional analysis studies and in the second stage, the selectivity towards oxidizing (nitrogen dioxide, NO₂) and reducing (NH₃, ethanol, methanol and hydrogen sulphide, H₂S) gases was tested. The sensor fabricated at 0 °C showed an optimum response of 26% to 100 ppm NH₃ gas, which was superior to those obtained for the sensors developed at 35 °C (19%) and −5 °C (23%). The as-developed low-temperature flexible gas sensor demonstrated fast response (19 s) as well as recovery time (36 s) periods, 99% reproducibility and good stability, revealing commercial application potential for example in industry where high temperature operation is prohibited. Impedance spectroscopy was used to investigate the plausible interaction mechanism of the NH₃ gas molecules with the flexible PAni. The operation of the NH₃ gas sensor device, fabricated on a laboratory scale, was tested and explored as a demo-video clip.

We demonstrate the preparation of cadmium sulfide (CdS) thin films via a facile chemical bath deposition method. The CdS films have been characterized by various techniques, such as, X-ray diffraction (XRD), energy dispersive X-ray (EDAX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Gas sensing performance of CdS thin films was tested at room temperature (38 °C) for oxidizing (NO₂, Cl₂) and reducing gases (H₂S, NH₃, C₂H₅OH, CH₃OH). CdS films were found to be highly selective and sensitive to NO₂ with a maximum response of 61% at 200 ppm with a fast response time of 50 s and 81% stability. Furthermore, the sensor is able to detect up to low (5 ppm) concentration of NO₂ gas with a reasonable response (5%). The plausible mechanism(s) of NO₂ sensing has been discussed.

Simple and inexpensive single step facile novel chemical route for the preparation of polyaniline (PANi) nanofibers has been reported. These PANi nanofibers are characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM). Polyaniline nanofibers exhibit amorphous nature as confirmed from XRD and SAED study. Based on FESEM and TEM analysis, the formation of the polyaniline nanofibers with average diameter of about 40 nm was inferred. The presence of characteristic bonds of polyaniline was observed from FTIR spectroscopy technique. Electrical and optical properties revealed that p-type conductivity PANi with room temperature conductivity of 2.77 × 10⁻⁵ (Ω cm)⁻¹ has band gap of 3.40 eV. A blue shift of 0.86 eV with characteristic absorption peak at 441 nm has been attributed due to quantized size of polyaniline nanofibers.

A nickel oxide (NiO) electrode has been synthesized electrochemically, which is envisaged for supercapacitor application. The structural, morphological, and phase-purity confirmation studies of NiO films were undertaken using X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy, and contact angle measurements. Films of NiO were amorphous in phase, as there were no reflecting planes in the X-ray diffraction pattern. The presence of characteristic bands in FTIR and X-ray photoelectron spectroscopy analysis corroborated the NiO structure. The NiO film surface was smooth with very fine elongated particles (∼70 nm) and hydrophilic in character (57°). The supercapacitive performance of an NiO electrode tested using cyclic voltammetry measurement in 0.5 M Na₂SO₄ electrolyte within the potential range of −1.2 to +1.2 V demonstrated a specific capacitance as high as 458 F g⁻¹ at 5 mV s⁻¹. The obtained specific energy, specific power and Coulomb efficiency of NiO electrode were 10.90 W h kg⁻¹, 0.89 kW kg⁻¹, and 98%, respectively.

Thin films of polyaniline (PANi) and PANi:titanium oxide (TiO₂) composites have been synthesized by sol—gel spin coating technique. The TiO₂ powder of particle size 50–60 nm was synthesized by sol–gel technique and the polyaniline was synthesized by chemical oxidative polymerization of aniline. The composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) Fourier transform infrared (FTIR) and UV-vis spectroscopy, and the results were compared with polyaniline films. The intensity of the diffraction peaks for PANi:TiO₂ composites is lower than that for TiO₂. The characteristic FTIR peaks of PANi were found to shift to a higher wave number in the PANi:TiO₂ composite. These observed effects have been attributed to the interaction of TiO₂ particles with PANi molecular chains. The room temperature resistivity of polyaniline:nano-TiO₂ composite is 3.43 × 10³ Ω cm and the resistivity of pure nano-TiO₂ particles is 1.60 × 10⁶ Ω cm.

We report for the first time a room temperature smart NH ₃ sensor based on PAni–Fe ₂ O ₃ nanocomposite loading on flexible PET substrate by in situ chemical oxidative polymerization method.