Title

Single-Molecule Interfacial Electron Transfer in Solar Energy Conversion and Bioremediation

Date of Award

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

H. Peter Lu

Second Advisor

Alexander N. Tarnovsky (Committee Member)

Third Advisor

John R. Cable (Committee Member)

Fourth Advisor

Andrew C. Layden (Committee Member)

Abstract

The present thesis describes the investigation of the factors affecting the electron transfer dynamics in the semiconductor-molecule and metal-molecule interfaces as well as the bacterial heavy-metal reduction on the cell surface of dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. The investigation of these systems was mainly performed by parabolic-mirror-assisted tip-enhanced near-field topographic-spectroscopic imaging, surface-enhanced Raman spectroscopy, and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. The influence of the surface states and the electric field on the charge transfer process and the interface properties was studied on TiO2-alizarin complex. It has been demonstrated that once alizarin is introduced to the TiO2 surface, the electronic delocalization occurs at the interface, suggesting the involvement of the surface states in charge transfer coupling. Moreover, it has been shown that the electric field significantly alters the coupling at the interface which is also expected to alter the electron transfer dynamics. Furthermore, the redox reactions at the silver-hemin interface has been probed by the prominent fluctuations of the Raman frequency of a specific vibrational mode, v4, which is a typical marker of the redox state of the iron center in a hemin molecule and suggested that the single-molecule redox reaction dynamics at the interface is primarily driven by thermal fluctuations. Lastly, the experimental data obtained in the investigation of Cr(VI) reduction through the outer membrane heme-proteins, MtrC and OmcA, of the metal-reducing bacterium Shewanella oneidensis MR-1 suggested that the direct microbial Cr(VI) reduction and Fe(II) (hematite)-mediated Cr(VI) reduction mechanisms may coexist and the cooperation of surface proteins, OmcA and MtrC, makes the reduction reaction most efficient.