Development of ZnO Nanotube Arrays for Chemical Sensing

The world today faces three interconnected issues: global warming, air pollution, and the rise in cancer rates. The common cause is the excessive use of fossil fuels. It has been widely recognized that net-zero emissions should be achieved before the year 2050. Hydrogen produced using renewable sources is a clean energy vector that could help the world achieve this goal. Nevertheless, hydrogen leakage can cause more global warming as it prolongs methane lifetimes in the atmosphere. Therefore, there is a need to promptly detect hydrogen leaks as its production and utilization increase with the paradigm shift in the energy system. At the same time, the increase in the overall cancer rates, which can also be correlated with environmental pollution, remains a critical challenge in global healthcare. Detection of volatile organic compounds (VOC) in exhaled gas that are cancer biomarkers is emerging as a viable approach for early-stage cancer detection. Gas sensing technologies, particularly those based on low-cost semiconductor metal oxides (SMOX), offer feasible solutions to both these problems. Nevertheless, the application of SMOX sensors in these areas faces challenges due to inadequate sensitivity to target species and cross-sensitivity to non-target species. In this dissertation work, we addressed these critical problems through the development of a new material, anodic ZnO nanotube array, as the sensing platform and the application of artificial intelligence to a sensor system developed using this material. The nanotube array geometry showed specific light scattering properties, as revealed by the finite difference time domain simulations, that are useful for the application of this semiconductor in solar devices. The density functional theory calculations showed distinct quantum conductance of the material. By using morphology-controlled synthesis and defect engineering and by applying machine learning algorithms to discriminate the response patterns of an array of sensors, we could achieve high selectivity, low detection limit, and low temperature of operation. This research demonstrated the potential of the material to be the platform for a single, affordable sensing technology to play dual critical roles: real-time monitoring of hydrogen in the environment and detection of breath VOCs for early-stage breast cancer detection.

Name thesis:degree_name

Doctor of Philosophy

Discipline thesis:degree_discipline

Physics

Grantor

University of Houston

Year dc:date.issued

2025

Author dc:creator

• Waligo, David 1994-

Advisor dc:contributor.advisor

• Varghese, Oomman K.

Committee members dc:contributor.committeemember

• Grabow, Lars C.
• Freelon, Byron K.
• Chen, Shuo
• Ting, Chin S.

• Breast cancer
• Electronic nose
• Sensor array

Language dc:language.iso

English

Handle dc:identifier.uri

https://hdl.handle.net/10657/20837

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/20837