Date of Award

Spring 1-1-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Gordana Dukovic

Second Advisor

Niels H. Damrauer

Third Advisor

Jennifer N. Cha

Fourth Advisor

Michael P. Marshak

Fifth Advisor

Garry Rumbles

Abstract

Artificial photosynthesis represents a promising strategy to capture and store solar energy through the production of carbon neutral fuels. This process begins with absorption of a photon by a semiconductor creating an electron-hole pair which are then separated and used to drive reduction and oxidation reactions. CdS nanostructures are model light absorbers for studying these charge transfer reactions and have already demonstrated photoinduced electron transfer to drive a variety of reactions. However, there has been comparatively little progress in understanding how CdS nanostructures may be used to sensitize oxidation reactions such as water oxidation. To this end, we undertook a thorough study of the excited state charge transfer behavior of a model system consisting of a mononuclear Ru water oxidation catalyst attached to the surface of a CdS quantum dot. Through careful analysis of the electron and hole sensitive measurements, we were able to determine parameters relevant for successful water oxidation. The first part of this dissertation consists of a study on the rate and efficiency of hole transfer to the catalyst. By modelling time resolved and steady state emission data it was discovered that the catalyst strongly binds to the quantum dot and engages in rapid photoinduced-hole transfer. The efficiency of hole transfer is limited only by competition with the tendency of holes to localize to quantum dot surface trap states. The second part of this dissertation determines the fate of the electron and hole following hole trapping or transfer. The population of quantum dots that transferred holes was found to decay to the ground state over the course of nanoseconds, while hole trapping appears to facilitate electron transfer to the catalyst. The final part of this dissertation explores the binding between quantum dot and catalyst using NMR spectroscopy. The two bind in a specific orientation which appears to facilitate hole transfer by provide a charge transfer pathway between the electronic states of the catalyst and quantum dot. This work establishes data analysis methods and design principles which may be leveraged in the development of future catalyst/quantum dot systems.

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