Research Overview

Research in the Knowles group seeks to develop fundamental understanding of the synthesis, chemistry, electrochemistry, and photophysics of metal oxide semiconductor nanomaterials. Metal oxide semiconductors are a richly diverse class of materials with optical, electronic, chemical, and magnetic properties that vary widely depending on composition and stoichiometry. We aim to contribute to rational strategies for improving the performance of these materials in applications related to solar energy capture and storage.

One of our primary goals is to understand structure-function relationships between the nanostructured morphology and surface chemistry of a metal oxide semiconductor film and its performance as a photoelectrode. In addition to studying nanostructured films fabricated by sol-gel and electrodeposition techniques, we also use colloidal metal oxide nanocrystals as dispersible model systems to study the inter-related impacts of size, shape, and surface chemistry on interfacial redox processes that occur in the dark and under illumination.

To enable these studies, we design and develop rational approaches to controlling the size and shape of metal oxide nanocrystals synthesized by solvothermal methods and explore new single-source molecular precursors that will enable synthesis of previously inaccessible metal oxide crystal phases under ambient pressure. We are particularly interested in developing new synthetic strategies to access ternary metal oxide nanocrystals that have desirable optical, electronic, and chemical properties but are difficult to synthesize in colloidal form. In all of these synthetic projects, we strive to understand the mechanisms by which precursors convert to nanocrystal monomers and monomers nucleate to form nanocrystals.

Students in the Knowles group gain interdisciplinary experience at the interfaces of physical, inorganic, and materials chemistry. In addition to standard techniques for characterization of solution-phase and nanostructured inorganic materials (i.e. electron microscopy, X-ray diffraction, and NMR, infrared, electronic absorption, Raman, and photoluminescence spectroscopy), the core techniques used in our lab include spectroelectrochemistry, photoconductivity, reflectance spectroscopy, and time-resolved optical spectroscopies.

Research Interests

• Inorganic Materials Chemistry

Selected Publications

• Shelton, J. L.; Knowles, K. E. Polaronic Optical Transitions in Hematite (α-Fe₂O₃) Revealed by First-Principles Electron-Phonon Coupling. J. Chem. Phys., 2022, 157, 174703.
• Beidelman, B. A.; Zhang, X.; Sanchez-Lievanos, K. R.; Selino, A. V.; Matson, E. M.; Knowles, K. E. Influence of Water Concentration on the Solvothermal Synthesis of VO₂(B) Nanocrystals. CrystEngComm, 2022, 24, 6009-6017.
• Sanchez-Lievanos, K. R.; Knowles, K. E.^* Controlling Cation Distribution and Morphology in Colloidal Zinc Ferrite Nanocrystals. Chem. Mater., 2022, 34, 7446-7459.
• Chakraborty, S.*; Schreiber, E.*; Sanchez-Lievanos, K. R.; Tariq, M.; Brennessel, W. W.; Knowles, K. E.; Matson, E. M. Modelling local structural and electronic consequences of proton and hydrogen-atom uptake in VO₂ with polyoxovanadate clusters. Chem. Sci., 2021, 12, 12744-12753. (*these authors made equal contributions to this work)
• Brewster, D. A.*; Koch, M. D.*; Knowles, K. E. Evaluation of electrochemical properties of nanostructured metal oxide electrodes immersed in redox-inactive organic media. Phys. Chem. Chem. Phys., 2021, 23, 17904-17916. DOI:10.1039/D1CP02370E. (*these authors made equal contributions to this work)
• Shelton, J. L.; Knowles, K. E. Thermally Activated Optical Absorption into Polaronic States in Hematite. J. Physical. Chem. Lett. 2021, 12, 3343-3351.