Date on Master's Thesis/Doctoral Dissertation

5-2022

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Degree Program

Chemistry, PhD

Committee Chair

Nantz, Michael H.

Committee Member

Fu, Xiao-An

Committee Member

Luzzio, Frederick A.

Committee Member

Zamborini, Francis P.

Author's Keywords

Au MPCs-based chemiresistors; MEMS; acetone; Cs-Cl interactions; BTEX; TCE

Abstract

The development of gas sensors for detection of volatile organic compounds (VOCs) has been of interest in the sensing field for decades. To date, the use of metal nanoparticle-based chemiresistors for trace VOC detection, particularly gold nanoparticle-based sensors, is of great interest due to their high chemical stability, ease of synthesis, unique optical properties, large surface to volume ratio, and high level of conductivity. Much effort has been devoted towards gold monolayer protected clusters (Au MPCs) as chemiresistors to detect harmful VOCs. The present thesis documents the results of our efforts to exploit the advantages of functionalized Au MPCs chemiresistors for selective VOCs sensing by changing Au MPCs surface functionality. Our concept is to incorporate binding motifs onto Au MPCs to selectively bind target VOCs and thereby improve the sensing capabilities of chemiresistors derived from casting the functionalized Au MPCs on interdigitated electrodes (IDEs). Chapter 1 in this thesis provides a review of nanoparticle-based chemiresistors for VOCs detection, the use of MEMS technology to prepare Au MPCs-based chemiresistors, and surface functionalized Au MPCs for VOCs detection. As inceptive studies, we were able to prepare urea-functionalized Au MPCs that demonstrated remarkable sensitivity and selectivity toward acetone serving as a representative carbonyl VOC. Chapter 2 describes the urea-functionalized Au MPCs approach for acetone sensing. We examined several structural elements of thiol urea ligands to change the degree of H-bonding between adjacent urea motifs on the Au MPCs surface as well as varied the steric properties of terminal groups on the urea-functionalized chains. The responses of the developed sensors were notably affected by the urea functional motifs. A tert-butyl end group on the thiol urea sensors resulted in high sensitivity and selectivity toward acetone and delivered a sensor capable of detecting acetone in air at concentrations from 10 ppb to 10 ppm. Next, we expanded our functionalized Au MPCs-based chemiresistive studies toward detection of aromatic VOCs. We explored metal carboxylate-functionalized Au MPCs chemiresistors as a means to selectively detect aromatic hydrocarbons, such as benzene, toluene, ethylbenzene, and xylene (BTEX), at trace levels in outdoor and indoor air. Here, we exploited the strong cation-π noncovalent interactions between metal cations bound to the Au MPCs-based chemiresistor surface and the π-systems of BTEX as a principal sensing mechanism. In this study, we synthesized alkali-metal carboxylate-functionalized Au MPCs by modifying the surface chemistry of Au MPCs via an oxime ether approach. Chapter 3 includes our alkali-metal carboxylate-functionalized Au MPCs chemiresistor synthesis and their selective binding strategy for aromatic VOCs capturing over non-aromatic VOCs. For our study, Li+, Na+, and K+ ion functionalized Au MPC sensors were developed. The K+- and Na+- functionalized Au MPCs sensors show a higher response to electron rich BTEX VOCs over electron deficient nitrobenzene, cyclohexene, acetone, and methanol vapors. Response of Li+ sensor for all the analytes were very low than the Na+ and K+ ion sensors. The developed sensors response to selected aromatic and non-aromatic VOCs suggests cation-π interactions arising between the positively charged cations and the electron-rich aromatic π-systems. The results open a promising research direction for harnessing cation-π interaction to create aromatic VOC-selective sensors. Chapter 4 details our primary investigation into the use of the unusual binding ability of a cesium cation to vicinal alkyl and vinyl chlorides to detect trichloroethylene (TCE). This chapter describes the sensor response patterns of cesium carboxylate-functionalized Au MPCs chemiresistors on exposure to different alkyl and vinyl chlorides to explore the influence of structural features on TCE detection. The developed Cs+-Au MPCs sensor exhibits a higher response to analytes with vinyl 1,2-dichlorounit than the other chloro analytes. Moreover, TCE exhibits a high sensor response at 1 ppm – 5 ppm vapor concentration than the other declared harmaful chloro analytes. Hence, this study revealed the different binding affinities of cesium cation toward the geminal, vicinal and vinyl halides and how it affects for sensor response. In summary, these results show that the outer ligand structure of thiolate-protected Au MPCs plays a major role in enhancing selectivity and sensitivity toward VOCs and suggests this approach as an effective means for targeting analytes.

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