Nanotechnology has the potential to revolutionize various fields, addressing complex issues such as cancer treatment, waste remediation, and energy storage. To achieve this, precise engineering of nanocrystals at the atomic level is essential, going beyond mere control of size and shape. The unique properties of nanomaterials, which differ from their bulk counterparts, are influenced by surface chemistry, defects, and local structure. These characteristics are determined by the synthesis methods used, making a deep mechanistic understanding of these processes crucial for engineering nanoscale structures and properties.
To contribute to the rapidly evolving field of nanoscience, this dissertation focuses on the solution-based synthesis of vanadium oxide nanocrystals. Vanadium oxides are promising candidates for applications in catalysis, sensing, cathode materials for high-density lithium batteries, smart windows, neuromorphic computing, and optical switching. However, vanadium oxides exhibit multiple oxidation states (+2 to +5) and polymorphs. Consequently, the colloidal synthesis of high-quality vanadium oxide nanocrystals in a specific oxidation state and stoichiometry remains challenging.
This dissertation advances the synthesis of vanadium oxide nanocrystals, emphasizing the effects of synthetic parameters on their oxidation state and crystal structure. Key findings include the successful synthesis of anosovite V₃O₅ nanocrystals via a hot-injection method, marking the first colloidal synthesis of this rare phase from a readily available precursor. By adjusting vanadium precursor-to-alcohol-to-amine ratio, controlled reduction of vanadium was achieved to selectively synthesize V₃O₅ and V₂O₃ nanocrystals. The dissertation also presents an alcohol-mediated valence-state controlled synthesis method for selective preparation of pure corundum-structured V₂O₃ and anosovite V₃O₅ nanocrystals. Comprehensive characterization, including spectroscopic ellipsometry and diffuse reflectance spectroscopy, reveals unique optical properties deviating from bulk behavior, attributed to the nanoscale size effects. In addition, a heat-up method was developed for synthesizing VOx nanocrystals by thermal decomposition of vanadyl acetylacetonate, demonstrating the formation of vanadium monoxide nanocrystals. The reaction pathways for the formation of these nanocrystals via hot-injection method and heat-up methods were analyzed with ATR-FTIR spectroscopy. The findings will advance the fundamental understanding of vanadium oxide nanocrystal synthesis and pave the way for their application as advanced functional nanomaterials.