Colloidal Metal Chalcogenide Quantum Dots as Photo-Redox Catalysts for Model Reactions Relevant to the Formation of Liquid Fuels

This document details a proposal to use light and colloidal semiconductor nanoparticles (or “quantum dots”, QDs) to catalyze a set of basic chemical reactions relevant to the production of liquid fuels. Many reactions that produce, or facilitate the production of, fuels – such as the reduction of CO2 to methanol or methane – require multiple electron reductions or oxidations of small-molecules. These “redox” reactions can be conducted even more sustainably by powering them with sunlight, through the use of a “photo-redox catalyst”. The long-term objective of this research is to develop metal-chalcogenide QDs into soluble, multi-active-site, colloidal photo-redox catalysts that surpass the performance of homogeneous and heterogeneous catalysts for the sustainable, solar-powered production of liquid fuels. In the next three years, we aim to demonstrate and study four basic types of fuel-production-relevant processes that (i) use the QD surface as a scaffold to bring reagents together, and (ii) manipulate the electronic structure of the QD excited state to provide electrons with sufficient energy to perform reactions without sacrificial reagents. Each of these processes exploits unique characteristics of colloidal QDs as photocatalysts, and each requires the QD to serve the roles of both light absorber and catalyst. In achieving the objectives detailed in this proposal, we will answer fundamental questions about proton-coupled charge transfer at the interface between semiconductor nanoparticle and a molecule, realize new surface chemistries for nanoparticles to adsorb catalytic substrates in reactive geometries, learn to control the density of protons and characterize molecule-molecule interactions on nanostructured surfaces, and, ultimately, move toward establishing quantum dots as the next class of high-performing photocatalyst for the production of liquid fuels.