MECHANISTIC DESIGN OF ELECTROSPUN METAL OXIDE SEMICONDUCTOR NANOFIBERS FOR TRACE LEVEL GAS DETECTION
Date of Award
2026
Document Type
Open Access Dissertation
Degree Name
Doctor of Philosophy in Chemical Engineering (PhD)
Administrative Home Department
Department of Chemical Engineering
Advisor 1
Yixin Liu
Committee Member 1
Michael M. Mullins
Committee Member 2
Lei Pan
Committee Member 3
Kathryn A. Perrine
Abstract
Metal-oxide gas sensors remain essential for environmental monitoring, industrial safety, and emerging smart-infrastructure applications. However, their widespread deployment is constrained by persistent challenges in selectivity, humidity tolerance, and long-term stability. Harsh operating environments, characterized by fluctuating humidity, interfering gas mixtures, and variable temperatures, can destabilize surface states and disrupt charge-transfer pathways, leading to signal drift and reduced sensing reliability. Emerging applications of gas sensing require trace-level detection, regardless of environmental operating conditions. Addressing these limitations requires a deeper understanding of how defect chemistry, heterojunction formation, and surface-state engineering collectively govern gas-sensing behavior. This dissertation advances understanding through two complementary research directions. The first explores p-type and mixed-phase architectures that leverage heterojunction-driven sensitization. Electrospun ZnO/CoMoO4/ZnCo2O4 composite nanofibers achieved ~ 50 times increase in n-butanol sensing compared to pristine ZnCo2O4 spinel. Also, 250 ppb n-butanol detection was achieved with a Limit of Detection (LOD) of 29 ppb. This illustrates how interconnected n–p–p junctions, catalytic transition-metal sites, and high-surface-area nanostructured morphologies synergistically amplify sensing responses while accelerating surface reaction kinetics. The second research direction investigates rare earth– doped SnO₂, focusing on how Sm³⁺ induced trap states influence electronic structure and sensing performance. Ultra-trace H2 detection at 25 ppb was demonstrated with a calculated LOD of 4.5 ppb. To further enhance humidity tolerance, Sm3+ and Tb3+ co-doping was examined for its effects on defect chemistry and electronic structure. Although co-doping improved gas sensitivity, only modest improvements in humidity tolerance were observed, ultimately identifying Tb-doped SnO2 as the most stable sensing configuration under humid conditions. Tb3+ strengthened metal-oxygen bonding, thereby improving the humidity resilience. Collectively, these studies demonstrate that engineered interfaces, whether through dopant-induced defect modulation or deliberate heterojunction design, play a central role in achieving reliable sensing under real-world conditions. By comparing rare-earth-modified SnO2 with advanced p-type materials, this dissertation establishes a unified framework linking defect chemistry, surface energetics, and interfacial charge transport to improved environmental stability and selectivity in metal-oxide gas sensors.
Recommended Citation
Fungura, Asky T., "MECHANISTIC DESIGN OF ELECTROSPUN METAL OXIDE SEMICONDUCTOR NANOFIBERS FOR TRACE LEVEL GAS DETECTION", Open Access Dissertation, Michigan Technological University, 2026.