Dissertation Defenses

Doctoral Dissertation Announcement

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Candidate: Junhyung Kim

Degree of: Doctor of Philosophy

Department: Chemistry

Title: Synthesis, Characterization, and Catalyst Applications of Gold Nanoparticles

Committee:
Dr. Dongil Lee, Chair
Dr. Michael J. Barcelona
Dr. Yirong Mo
Dr. Gellert Mezei
Dr. Nora Berrah

Date: Monday, March 31, 2008 9:00 a.m. – 11:00 a.m.
1710 Wood Hall

Abstract:
Properties of nanometer-sized gold(Au) particles, especially those that are protected by a monolayer coating of thiolate ligands so called 'Monolayer Protected Clusters' (MPCs), are of intensive multidisciplinary interest for their potential applications in catalysis and electronics due to their size dependence.
In the core diameter larger sizes ( >1.5nm) AuMPCs show metallic behaviors in the electrochemical measurements. On the other hand, sub-nanometer (≈1.1nm) AuMPCs exhibits molecule-like electronic behaviors in typical Au38 nanoparticles. The various alkane chain thiols(C4S-C12S) capped Au38MPCs have been examined with the independent analytical tools, producing a remarkably consistent picture of these materials.
A greater understanding of the electron transfer dynamics, pathways in the different types of chemical structure and/or surrounding environments of the AuMPCs solid state as well as in the two dimensional (2D) arrangement is important in rationalizing electron transfer phenomenon in fuel cell catalyst, fabricating microelectronic devices, and sensors. MPC-based Langmuir monolayers offer particular virtues for the investigation of structural and electronic properties of 2D arrays. Because advantages of this Langmuir technique include establishing limiting nanoparticle area, easy manipulation of the monolayers, and interparticle distance control. The latter is of great significance because much of the attention in AuMPCs has been focused on correlation between interparticle distance and electronic and optical properties.
To extend charge transfer study, the charge transfer quenching of photoexcited semiconductor (TiO2) by hexanethiolate AuMPCs with core diameters of 1.1-4.9 nm was employed. The quenching efficiency of AuMPCs was compared using Stern-Volmer plots. The quenching constants (Kq) taken from slopes of the plots reveal that Kq increases from 5.6 105 to 4.09 107 by more than 70-fold as the core diameter increases from 1.1 to 4.9 nm. The origin of the size dependence is considered. Kq was found to linearly correlate with the MPC capacitance. This suggests that the quenching process is dominantly controlled by the capacitance of the electron acceptor (AuMPC).
Electrochemical properties of AuMPCs in the electrolyte solution, correlation between electron transfer dynamic and interparticle distance in the AuMPCs Langmuir monolayer, and charge transfer between semiconductor and AuMPCs study will be presented.