Abstract
Over the past few decades, the use of fossil fuels has generated greenhouse gases, resulting in increasing deleterious effects on our environment. Recently, research for alternative fuels has increased and has demonstrated positive advances towards processes such as artificial photosynthesis, CO2 reduction, and water splitting. Photocatalysis for the purpose of converting to these greener fuels is one of the main methods by which the products of these processes are achieved. Many types of materials can be used for this goal, particularly semiconductor nanomaterials and molecular catalysts. Fortunately, semiconductor nanocrystals (NCs), quantum dots (QDs) in particular, have several advantages, making them good materials for photocatalysis. They are efficient light harvesters, size tunable, and their surface chemistry can be manipulated towards improving the performance of the nanocrystal. The surface chemistry (ligands, etc) of QDs can control nanocrystal growth, solvent solubility, and electronic passivation, which dictate charge transfer properties in the NC. This work investigates how different molecules bound to the QD surface affect electron transfer processes with the purpose of CO2 reduction with a molecular catalyst. The first project details how electron transfer from a Cd3P2 QD to a molecular catalyst, fac-Re(4,4′-R2-bpy)(CO)3Cl (bpy=bipyridine; R=COOH) (ReC0A), is changed upon the addition of a hole scavenger, triethylamine (TEA). ReC0A is highly selective and efficient for catalyzing CO2 reduction under only 400 nm excitation. By using a Cd3P2 QD, which can absorb into the near IR, and reducing the ReC0A catalyst, we can extend the range over which CO2 reduction can occur. The second project describes the Fano resonance (FR) coupling phenomenon that occurs between CdSe QD intraband transitions and ReC0A CO modes as a function of catalyst concentration and QD size. The third work demonstrates the effect of distance on FR coupling using ReCxA catalysts with different chain length linkers and core/shell CdSe/ZnS QDs. Finally, the last project is a collaboration with Hong Kong City University that investigates hot electron transfer in Ag-CdSe heterostructures resulting in high quantum yield. This thesis work demonstrates charge transfer dynamics in NC-molecular catalyst complexes upon ultrafast laser excitation for the application of CO2 reduction and photocatalysis.
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