Technological development has enriched human life and made it more comfortable and convenient. However, the industries established to produce various devices and products have negatively impacted the environment. Industrial production outsources multiple types of pollutants mainly air pollutants that harm humans as well as the environment. In general, gases such as ammonia (NH3), hydrogen sulphide (H2S), carbon monoxide (CO), nitrogen dioxide (NO2), sulphur dioxide (SO2), carbon dioxide (CO2), and nitric oxide (NO), etc. are considered the most harmful gases which released from various processes [1, 2]. Ammonia (NH3) is a hazardous gas that is commonly found in the atmosphere as a result of chemical processes, fertilizer use, material processing, refrigeration, and other sources [3, 4]. Exposure to ammonia can have various adverse effects on the human body, including damage to the respiratory and cardiac systems, as well as the skin and eyes [5]. Therefore, to protect from these pollutants their quantitative detection with time being is the utmost necessity for precaution [6]. Worldwide various research groups have been working to develop a sophisticated and affordable gadget for widespread use by large-scale users for detection of gases [7]. A gas sensor is an analytical device that promises to detect harsh pollutant gases qualitatively and quantitatively [8]. The ability of sensors to operate at room temperature (RT) is highly desirable, as it is crucial for detecting harmful gases in the surrounding air [9]. In real-world scenarios, these sensors play a vital role in detecting and tracking harmful gases, making real-time operation essential for practical applications [10]. Therefore, in the realm of scientific research and technological advancement, it is imperative to develop gas sensors that meet these rigorous standards [11].
The selection of materials with desired properties is crucial when fabricating gas sensors for practical applications. Several criteria decide the choice of gas sensing material, including operating environment, sensitivity, target gas, cost, etc. Recently, a variety of materials have been utilized in the development of gas sensors including metal oxides, conducting polymers, carbon materials, and more. Among these, conducting polymers are widely used in gas sensors due to their unique physicochemical properties which enhance the sensing parameters such as high sensitivity, selectivity, stability, detection limit as well as operation at room temperature, etc. The family of conducting polymers enriched with the candidates including polyaniline (PANI), polypyrrole (PPY), polythiophene (PTh), etc. Particularly, in gas sensing applications PANI is used extensively due to its excellent properties i.e. tuneable electrical conductivity, redox property, larger surface area, high flexibility, outstanding stability at ambient conditions, cost-effectiveness, and ease of fabrication, etc. However, PANI suffers from low mechanical strength, which adversely affects its sensitivity and specific selectivity [12–14].
The major issue associated with PANI use in gas sensors can be resolved by doping with various organic and inorganic materials. The proper doping enhances the mechanical strength of PANI and creates more active sites by altering its structure [15, 16]. Integrating inorganic nanoparticles into PANI can dramatically enhance the sensitivity, selectivity, and overall performance of gas sensors. The synergistic effect of inorganic nanoparticles and PANI increases surface area and tuned electrical conductivity, improves catalytic activity, stability, durability, and enhances the charge transfer ability [17, 18]. Recently, zinc oxide (ZnO), titanium dioxide (TiO₂), and iron oxide (Fe₂O₃) as inorganic nanoparticles were incorporated into PANI to detect NH3 [19, 20]. ZnO is a highly intriguing option for gas sensing applications because of its unique properties including a wide direct band gap, high exciton binding energy, biocompatibility, non-toxicity, high chemical stability, strong electron transfer capability, and exceptional mechanical strength [21, 22] However, ZnO-based gas sensors have trouble operating at room temperature [23].
Thus, the PANI-ZnO nanocomposite has paved the way to enhance gas sensor parameters even at room temperature. Recently, Kaur, R. et.al. reported the PANI-ZnO nanocomposite with varying concentrations of ZnO nanoparticles for ammonia detection. The developed sensor shows a response of 1.43–25.24% for 5–200 ppm with 5 ppm as the lower limit of detection and 18 s as the response time at the temperature range 20–100°C [24]. In another study, Bai, Y. presented a ZnO/PANI film prepared by spraying ZnO nanorods synthesized using the hydrothermal method to detect NH3 at room temperature. The film detected concentrations of 0.1–100 ppm of NH3, with the response value doubling to 12.96 for 100 ppm NH3 and the recovery time shortening to 31.2 seconds, which is 1/5 of the original time [25]. The research conducted by Karmakar, N. involved developing nanocomposite polyaniline (PANI) films with varying concentrations of ZnO and studying their ability to detect ammonia gas. They found that loading 10 at% ZnO in PANI resulted in a gas sensing response of 59% for 120 ppm NH3 gas. Additionally, they embedded Ag-decorated ZnO nanorods in the PANI matrix using the in-situ oxidative polymerization technique, which showed a response of 70% at 120 ppm and a recovery time of less than 120 s [26].
Here, we have presented PANI-ZnO nanocomposite films with varying concentrations of ZnO for NH3 detection. The physicochemical and optical properties of PANI and PANI-ZnO thin films were explored, along with NH3 detection. The study demonstrated that the sensing parameters of the PANI-based sensor can be improved by doping ZnO nanoparticles significantly