Author ORCID Identifier

https://orcid.org/0009-0001-3549-1634

Semester

Spring

Date of Graduation

2025

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Alan Bristow

Committee Co-Chair

Lian Li

Committee Member

Lian Li

Committee Member

Tudor Stanescu

Committee Member

Marimuthu Andiappan

Abstract

Photocatalysis, a promising method for solar-to-chemical energy conversion, relies on sunlight to generate excited charge carriers in catalysts with sufficient lifetimes and mobilities to drive photoreactions. Thin-film semiconductors are essential for reducing charge recombination and enhancing mobility but suffer from a low surface-to-volume ratio problems, resulting in a reduced absorption coefficient and limiting solar-energy-conversion efficiency. Nanostructures address these limitations by enhancing light absorption and surface reactivity. However, efficient photocatalysis also requires that the semiconductor’s band edges align with the redox potential of the desired photoreaction, limiting light absorption to just some of the whole solar spectrum. In hybrid and composite photocatalysts utilizing noble plasmonic metal nanostructures (PMNs) and metal oxides, PMNs facilitate plasmonic resonance, while the semiconductor component enables band-gap-assisted redox reactions. However, the high expense and scarcity of noble metals presents significant cost issues for the process. Alternatively, dielectric Mie resonance-enhanced photocatalysts employ a single metal oxide (non-toxic and abundant in nature) that supports both dielectric resonance behavior and band-gap-assisted redox reactions, significantly enhancing light matter interactions. These Mie resonance effects are highly shape- and size-dependent and arise due to electromagnetic dipole and higher-order multipole coupling. This dissertation investigates the ultrafast charge-carrier dynamics in Cuprous Oxide (Cu₂O) nanoparticles (NPs), exhibiting Mie resonances, using transient absorption (TA). The observed protracted negative delay time signal in the TAS data, associated with perturbed free induction decay (PFI), highlights coherent effects in Cu₂O NPs. We examine the influence of size- and shape dependent PFI contributions on photocatalytic performance and analyze how the clustering induced scattering effects of Cu₂O nanocatalysts impact photocarrier concentration estimations, recombination, and relaxation dynamics. Further, this thesis explores the photocarrier dynamics in Palladium (Pd)-coated Cu₂O nanocatalysts, forming a Cu₂O-Pd heterostructure. The Schottky barrier at the Pd-Cu₂O junction facilitates charge separation and reduces recombination, significantly enhancing carbon-carbon coupling reactions under ambient conditions—reactions that typically require high-energy conditions. This phenomenon is characterized through transient reflection (TR) and analyzed using rate equation inversion, band alignment calculations, two-temperature model to assess Fermi smearing, and rate transfer calculations. Finally, we present an operando study of photocarrier dynamics in Cu₂O nanocatalysts during active reverse water-gas shift reactions using TR. This novel approach captures nanocatalyst behavior under real reaction conditions. Detailed descriptions of the experimental setups and methodologies are included to provide a comprehensive framework for advancing photocatalysis research.

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