Flame Synthesized Nanoparticles and Miniaturized Opto-electronic Devices for Advanced Gas Sensing

Abstract

Advancements in gas sensing technology are crucial for enhancing environmental safety, industrial monitoring, and health diagnostics. This research explores the transformative potential of flame-synthesized metal oxide nanoparticles and miniaturized opto-electronic devices in creating highly sensitive and selective gas sensors. The study delves into optimizing flame spray pyrolysis for developing nanostructured materials, with a focus on manipulating process parameters to refine the physical properties of nanoparticles for enhanced sensing capabilities. A pivotal advancement is the promising strategy of engineering oxygen vacancies in thick semiconductor films using deep ultraviolet photoactivation. This method significantly enhances the room-temperature detection capabilities for volatile organic compounds, exemplified by the enhanced sensitivity and decreased response times of ZnO sensors to ethanol. Specifically, the introduction of oxygen vacancies by low temperature deep ultraviolet photoactivation leads to about a 58% increase in ZnO sensitivity, coupled with a 51% and 64% reduction in response and recovery times, respectively. The approach demonstrates a broader potential for tuning electronic structures and surface activities of semiconductor sensors, achieving lower detection limits (as low as 2 ppb) and improved selectivity at relatively low operating temperatures. Further innovations are realized in the engineering of three dimensional nano-heterojunction networks. By incorporating oxygen vacancies into NixOy-ZnO nanoscale heterojunctions through deep ultraviolet photoactivation, the sensing performance is significantly boosted. This results in an 88% increase in sensitivity to ethanol and a 30-fold enhancement in selectivity against a range of volatile organic compounds at room temperature. The heterojunctions, characterized by their high porosity and efficient charge separation, facilitate deeper penetration and interaction with target gas molecules, leading to unprecedented sensitivity and selectivity levels. Theoretical analyses corroborate these findings, showing a substantial increase in analyte adsorption energy due to the presence of oxygen vacancies. The research further culminates in the development of an innovative dual-sensing approach through the integration of plasmonic and electrical sensing in a single metamaterial sensing device. This multifunctional sensing platform, combining chemiresistive and plasmonic techniques, is a significant leap forward in gas detection technology. It leverages the unique properties of a zinc oxide and gold nanoparticle-based metamaterial, achieving simultaneous detection and discrimination of various volatile organic compounds. The dual-sensing system is further augmented by machine learning models capable of accurately predicting gas types with 32% accuracy and concentrations with a coefficient of determination (R2) of 0.96. This approach not only demonstrates exceptional sensitivity and selectivity but also opens new avenues for smart sensor applications in environmental, industrial, and health sectors. Overall, this research represents a substantial contribution to the field of chemical and gas sensing technology, offering innovative approaches for the development of highly sensitive, selective, and multifunctional sensors. The findings underscore the potential of nano-engineered materials in advancing smart sensor technologies, with significant implications across various domains including environmental monitoring, industrial safety, and health-related applications.