DESIGN AND DEVELOPMENT OF ZNO-BASED GAS SENSORS FOR AMMONIA DETECTION

Abstract

Chemiresistive gas sensors are attracting much attention due to their potential in the development of gas monitoring technologies. However, their widespread practical deployment remains limited by the suboptimal performance of conventional sensing materials, particularly metal oxides which typically require high operating temperatures. This thesis work presents a comprehensive investigation into the characterization, design, and synthesis of composite fibrous sensing materials, with a particular emphasis on metal oxide-based systems. By incorporating ZnO into fibrous structure and strategic doping approaches, such as Ti-doping into ZnO matrices, the study demonstrates significant improvements in gas sensing performance, including reduced operating temperatures and enhanced sensitivity. The research highlights how the fibrous composite structure, achieved via electrospinning, contributes to increased surface area, mechanical flexibility, and stability, ultimately paving the way for the development of low-power, flexible, and wearable chemiresistive gas sensors. Also, development of high-performance fibrous gas sensing materials based on Ti-doped ZnO for flexible ammonia sensors. A systematic investigation was conducted on ZnO materials doped with varying concentrations of Ti (x = 0.01, 0.02, 0.03, and 0.05), aiming to understand the correlation between composition, structural modifications, and gas sensing behavior. Among all samples, Zn0.98 Ti0.02 O demonstrated the best performance, achieving a notable response of 35% to 50 ppm ammonia at 70 °C working temperature which reduced from high 110 °C to ambient conditions. This improvement is ascribed to the higher surface area and improved adsorption/desorption, as confirmed by SEM and BET analyses. To realize real-world applicability, the Ti-doped ZnO was integrated into a fibrous composite structure via electrospinning, yielding a flexible sensor capable of maintaining excellent mechanical stability across a wide range of bending angles (0–90°). Structural and morphological characterizations using XRD, XPS, SEM, and TEM confirmed the successful incorporation of Ti and preservation of the ZnO crystal integrity. The study highlights the role of Ti doping in reducing electrical resistance, enhancing surface activity, and enabling mechanical flexibility, offering a viable pathway toward the advancement of flexible ammonia gas sensors.