Tuning the Optical and Catalytic Properties of CuO and Fe 2O3 Nanosheets for CO2 Conversio

The power of nanomaterials lies in our ability to control them. Copper oxide (CuO) and iron oxide (Fe2O3) are two non-hazardous materials, composed of earth abundant elements, whose nanoforms offer excellent opportunities for property tuning. Already these nanomaterials are being investigated for use as catalysts for CO2 reduction and water splitting, as absorbing layers in solar cells, and as active ingredients in hydrophobic and antimicrobial coatings. However, despite the wealth of research, controlling the fundamental properties of these materials remains a challenge. Incomplete characterization has led to irreproducibility and poisons otherwise exciting results inhibiting further progress.;What is the band gap of CuO? Not only is this an important fundamental question about the material, but also critical if it is to be used in any application that requires the absorption of light. For other materials this is an easily answerable question, however an investigation of the CuO literature yields results ranging from 1.1 to 2.6 eV for the bulk and nanomaterial alike. This widespread, though rarely acknowledged, controversy acts as the basis for the first part of this work. Taking CuO nanosheets as a model system, small perturbations in the surface oxygen content are made through a thermal oxidation post treatment in order to try to replicate the wide range of band gaps seen in the literature. With the aid of molecular modelling, fundamental structure-property relationships are established allowing for precise control of the band gap. Additionally, a correlation is found between band gap and reactivity in treated CuO nanosheets, a useful property-property relationship for studies in catalysis and photoelectrochemistry. Finally, a mechanism for these structural changes is proposed and supported using isotopic oxygen studies.;In the second part of this work the properties of OD-, 1D-, and 2D hematite are explored and compared. With a new spin on an old technique, hard templating is implemented using CuO nanosheets as a template to synthesize a new material: ultrathin polycrystalline hematite nanosheets. The band gap of these hematite nanosheets was found to be similar to that of hematite nanowires (approximately 2.1 eV), but less than that of nanoparticles (2.46 eV). Catalytic studies were also performed, examining how active each of these materials are in reducing CO2 via the reverse water gas shift reaction. The nanowires and nanosheets were both found to be excellent catalysts, reaching a CO2 conversion of 55% with selectivity of nearly 100%, while the nanoparticles showed poor activity. Once again, a link is shown between structure and properties as well as between optical and catalytic properties. Finally, molecular modelling is combined with temperature programmed experiments to provide a mechanistic understanding as to why the properties of these materials differ.;This work serves to showcase the link between structure and properties as well as the link between properties in copper and iron oxide nanosheets. It seeks to rectify some of the irregularities and contradictory reports for the band gap of CuO with an aim to better control the material's property. It puts forth new synthesis strategies for new 2D materials that act as a springboard for future investigations. It provides alternative routes for CO2 reduction and stresses the importance of computation paired with experiment to obtain a deeper mechanistic understanding of nano-metal oxide systems. Finally, this work--and I through it--hope to provide a window into the journey of a Ph.D. for any with a curious and contemplative mind.