Microwave gas sensor technology : developing graphene oxide-polyaniline nanocomposites for improved sensing and detection of ammonia gas

Over the past decade, ammonia gas sensors have received significant attention as robust platforms for many applications, including emission control, food safety, and monitoring patients' exhaled breath for the early detection of metabolic disorders. Particularly, to diagnose diseases such as dysfunction of the kidney and the liver, ammonia gas is a key biomarker present in human breath. This thesis explores the development of a microwave-based split-ring resonator (SRR) sensor with enhanced sensitivity to detect ammonia gas at low concentrations. The sensor is based on a nanocomposite fabricated by incorporating carbon-based nanomaterial into polyaniline (PANI) via the in-situ polymerization of aniline monomers. The addition of carbon-based materials, as a substrate and dopant to PANI, results in high sensitivity for low concentrations of ammonia gas, in a 150-400 s time interval at room temperature. The selectivity of the prepared sensor toward ammonia gas was tested in the presence of other higher concentrations of hazardous gases and a wide range of relative humidity levels (3 to 90%). The developed low-cost and robust sensor has the potential to monitor ammonia gas in various applications, including medical, environmental, food, and agricultural sectors. Although several studies have been carried out on the application of graphene oxide-polyaniline (GO-PANI) nanocomposites no scientific understanding of the interaction mechanism of GO-PANI and ammonia gas molecules has been investigated. Therefore, in the next step of this research, we monitored and analyzed the microwave gas sensor's response to ammonia gas to gain a better understanding of the interactions and mechanism. The time-dependent sensor response revealed that the Interactions of ammonia gas with polymer surface occurred via chemisorption or physisorption through the Langmuir adsorption mechanism. According to the designed thickness experiment, the thickness of sensitive elements affects the sensitivity of microwave gas sensors toward ammonia gas at the constant surface area, temperature, and humidity, supporting the role of absorption in the sensor's response.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat