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Exploiting the optical properties of earth abundant cuprous oxide nanocatalysts for energy and health applications

Addanki Tirumala, Ravi Teja
In this dissertation, we explore the optical properties of semiconductor materials, for energy and photocatalytic applications. In the past semiconductor materials used in photocatalytic reactions are prominently known through electron transfer mechanisms such as redox reactions, and local surface plasmon resonance (LSPR). In this work, we show substantial understanding and advantages of Mie resonances-based photocatalysis. Mie resonance-based photocatalytic mechanisms can find various applications in chemical manufacturing, pollution mitigation, and pharmaceutical industries. We developed an understanding that Mie resonances of metal-oxide nanoparticles are affected by material properties such as absorption and scattering coefficients, dielectric permittivity physical properties like geometry, size of these nanoparticles, and wavelength, and intensity of the incident light. In this work, we experimentally, demonstrate that the dielectric Mie resonances in cuprous oxide (Cu2O) spherical and cubical nanostructures can be used to enhance the dye-sensitization rate of methylene blue dye. The Cu2O nanostructures exhibit dielectric Mie resonances up to an order of magnitude higher dye-sensitization rate and photocatalytic rate as compared to Cu2O nanostructures not exhibiting dielectric Mie resonances. We further established structure-property-performance relationships of these nanostructures and experimentally found evidence, that rate of dye sensitization is directly proportional to the overlap of absorption characteristics of the nanocatalyst, absorption of the dye, and the wavelength of incident light. This work has the potential to be used in pollution mitigation applications, Dye-Sensitized Solar Cells, etc. Gaining a deeper understanding of the characteristics of Cu2O nanostructures, we have experimentally observed that tuning selectivity and activity of reactions can be achieved by modulating the incident wavelength of light. We performed intensity-dependent studies for methylene blue degradation for gaining mechanistic insights into selective photocatalysis. We explored C-C coupling reactions with small molecules which find applications majorly in the chemical and health industry. Carbon-carbon (C-C) coupling reactions are widely used to produce a range of compounds including pharmaceuticals, aromatic polymers, high-performance materials, and agrochemicals. For these reactions industrially, homogenous palladium (Pd) catalysts are used at high temperatures and are a solvent-intensive process. Palladium is expensive, toxic, and rare earth metal. However, the identification of truly heterogeneous versus homogeneous catalytic conditions remains an ongoing challenge within the field. In this research, we gained insights into the homogenous versus heterogeneous pathways using various analytical, experimental, and computational techniques. In this work, we found that Cu2O nanoparticles can catalyze C-C coupling reactions under ligandless and base-free conditions via a truly heterogeneous pathway paving the way for the development of highly efficient, robust, and sustainable flow processes.