Date on Master's Thesis/Doctoral Dissertation

5-2023

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemical Engineering

Degree Program

Chemical Engineering, PhD

Committee Chair

Fu, Xiao-An

Committee Co-Chair (if applicable)

Jaeger, Vance

Committee Member

Jaeger, Vance

Committee Member

Nantz, Michael

Committee Member

Sathitsuksanoh, Noppadon

Committee Member

Sumanasekera, Gamini

Author's Keywords

VOCs; sensor; microreactor; BTEX; Trichloroethylene; preconcentrator

Abstract

There has been a growing interest to measure volatile organic compounds (VOCs) in a range of environmental applications. The presence of toxic VOCs in the air has been associated with serious health problems including asthma, central nervous system dysfunction, cardiovascular disease and cancer, etc. Different analytical instruments such as gas chromatography-mass spectrometry (GC-MS) and sensor systems, such as metal oxide sensors are used to analyze VOCs. However, challenges still exist in the detection of airborne VOCs because of their trace concentration and interference with complex gas mixtures. In this dissertation, two microfabricated devices, a sensor array and a micropreconcentrator were investigated for both detection and quantitative analysis of toxic VOCs in environmental air. First, the microfabricated sensor-array has been developed for the simultaneous testing of multiple sensors. Alkali metal carboxylate-linked gold monolayer protected clusters (Au MPCs) have been investigated to selectively sense aromatic and chlorinated VOCs. Cation–π interaction towards the electron-rich aromatic region and electron-deficient cations such as Li+, Na+ and K+was explored to develop a sensor for aromatic compounds. Furthermore, Cs+-linked Au MPCs were utilized to develop a sensor for trichloroethylene because of Cs+ and Cl⁻ coordination. The nature of the interaction of these sensors with humidity led us to design and use a preconcentrator to trap the analyte of interest and to thermally desorb the captured compounds for producing moisture-free concentrated target VOC samples. Next, a microfabricated micropreconcentrator (μPC) was developed to enable the detection of trace target VOCs by the sensor array and eliminate moisture interference. Carboxen 1000 adsorbent was loaded inside the μPC to capture benzene, toluene, ethylbenzene and xylene (BTEX) and trichloroethylene. The performance of the μPC has been characterized and integrated with solid-phase micro-extraction (SPME) to improve signals for GC-MS analysis. Furthermore, a novel dual-compartment μPC has been developed to capture a wide range of VOCs. This microdevice contains two different sorbents – Carbopack X for trapping aromatic VOCs and silica gel coated with O-2,3,4,5,6-pentaflurobenzyl hydroxylamine (PFBHA) for capturing carbonyls via oximation. The captured compounds were eluted with dichloromethane and analyzed by GC-MS. About 90% of recoveries have been achieved for BTEX, formaldehyde, acetaldehyde and acetone. Finally, this microdevice was used for detecting BTEX and carbonyls at different locations in Louisville, KY. The combination of this dual-compartment μPC with our developed sensor-array could satisfy the demand for a portable system in the application of air quality monitoring and disease diagnostics from exhaled breath.

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