Date on Master's Thesis/Doctoral Dissertation

12-2011

Document Type

Master's Thesis

Degree Name

M.S.

Department

Chemistry

Committee Chair

Zamborini, Francis Patrick

Author's Keywords

Electronic nose; Au nanoparticles; Sensing; Volatile organic compounds; Chemiresistive; Electron hopping

Subject

Chemical detectors; Olfactometry; Nanoparticles

Abstract

This thesis describes 1) the kinetics of vapor phase place exchange reactions on films of gold monolayer protected clusters (Au MPCs) to alter the functionality of the Au MPCs, 2) applications of the reaction for altering chemiresistive sensing selectivity for volatile organic compounds (VOCs), and 3) the fabrication of a chemiresistive electronic nose for detecting VOCs based on sensor arrays and vapor phase place-exchange reaction. The motivation of this work was to develop a simple and effective method to synthesize and functionalize films of Au MPCs for applications in nanoelectronics, sensing, and catalysis. We first synthesize hexanethiolate-coated gold monolayer-protected clusters (C6S Au MPCs) and then prepare a film by drop-cast deposition. Placing the film of C6S Au MPCs into a closed container with mercaptoethanol leads to the replacement of the hexanethiolate ligands with mercaptoethanol ligands by vapor phase place-exchange. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy allowed a determination of the reaction kinetics. After one day of exchange, up to 91 percent of the hexanethiolates (C6S) were replaced with mercaptoethanol (OHC2S). The resistance of the films decreased from 250 MQ to 150 MQ after the one-day exchange. Importantly, the chemiresistive sensing response ratio to isopropanol (IPA) versus toluene gradually changed from 0.3 (lPA/TOL) for pure C6S Au MPCs to 1.8 after exchange with mercaptoethanol (91 %). In addition to mercaptoethanol, we exchanged films of C6S Au MPCs with mercaptopropionic acid (MPA) and mercaptopropyltrimethoxy silane (MPTMS) for building a sensor array consisting of four devices to detect various VOCs, including toluene, IPA, ethanol, and acetone with improved selectivity and recognition. These electronic nose devices, created through vapor phase place exchange reactions, generate a unique response pattern for each of the vapors, allowing us to differentiate them by pattern recognition methods. This study indicates that vapor phase place exchange reactions have broad potential applications in selective vapor sensing. The vapor phase place exchange reaction can be used for mass production of films of metal MPCs with various functionalities. There are several benefits over solution phase place exchange or direct synthesis of Au MPCs with different functionality, such as it is simple, fast, massively parallel, allows functionalities that would not be possible in solution, and provides control over the extent of exchange from 0 to almost 100%. Potential future applications include synthesizing metal MPC catalysts, electronic sensors, and chemical separators easily with low cost.

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