Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    Hybrid plasmonic tubular nanostructures: synthesis, optical and photoelectrocatalytic property
    (2022) Zhang, Qian; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Utilizing sustainable and clean solar energy in the visible-NIR range to drive chemical transformation has been a key resolution to solve the energy crisis. Recently, rational design of photocatalysts that conjugate plasmonic nanostructures with catalytic metal nanostructures has attracted particular research interests. This dissertation describes the design principles of plasmonic-catalytic hybrid tubular nanostructures and investigates their application in photoelectrocatalytic reactions.First, we introduced the mechanism of plasmon-mediated catalysis and current research of plasmonic photocatalysts. Specifically, managing the energy flow from the plasmonic entity to the catalytic entity is the crucial part for customizable design of photoelectrocatalysts. We also summarized the design principles of general electrocatalysts and synthesis of hollow nanostructures. Second, we reported a facile but highly reproducible synthetic strategy to fabricate catalytic Pt hollow nanotubes (NTs). Scalable fabrication of ultrathin Pt NTs can be achieved through simple mediation of the concentration of the surfactant employed in the reaction. Third, we reported a template-directed synthesis of PtAu NTs with tunable localized surface plasmon resonance (LSPR) bands in the visible-near infrared region (NIR). The geometric dependent LSPR band shift was systematically studied based off the spectra from both experiment and finite-difference time-domain (FDTD) simulations. It was found that the PtAu NTs exhibited the LSPR characters of both rodlike and hollow nanostructures. Finally, we investigated the photoelectrocatalytic performance of the PtAu NTs under visible-NIR light irradiation. The optimized photocatalytic activity of the PtAu NTs towards the electrooxidation of methanol was achieved by maximizing their LSPR absorption cross sections at longer wavelengths in the visible-NIR region. Meanwhile, combining the superior intrinsic electrocatalytic performance of PtAu NTs towards methanol oxidation, we expected the bimetallic PtAu tubular nanostructure could effectively convert visible light energy to drive the electrochemical transformation.
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    Toward Optimization of Photomodulation of Azobenzene-modified PPV Derivatives
    (2007-10-01) Grimes, Amy Frances; English, Douglas S; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Photophysical characterization of a family of photoswitchable conjugated polymers is presented in this work. Additionally the instrumentation constructed for these studies, a time-correlated single photon counting spectrometer, is discussed along with the methods used to characterize the instrument. Sample data and fitting procedures are presented. Overall instrument capabilities are also presented, specifically the use of the spectrometer to measure time-resolved fluorescence anisotropy. An example study probing the interactions between charged fluorophores and surfactant vesicles is included as a demonstration of a time-resolved fluorescence anisotropy application. Understanding the effect of side chain modifications on the emission of light from conjugated polymers is useful in the design of new polymers for applications in sensing and photovoltaics. This thesis focuses on determining the photophysical interactions between a photochromic side chain, azobenzene, covalently bound to a poly(p-phenylenevinylene) (PPV) derivative. Time-resolved and steady-state fluorescence measurements were employed in these studies. The photochromic azobenzene quenches emission from the PPV backbone differentially in its' two isomeric states. Both static quenching and non-radiative energy transfer were found to play important roles in the differential quenching of PPV emission by azobenzene. These studies led to the definition of a parameter to judge degree of difference in quenching between the two isomeric forms. This parameter, modulation efficiency (Emod), serves throughout the studies as an important figure of merit for the depth of modulation observed for structurally modified derivatives of the original azobenzene-modified PPV derivative. Maximizing the modulation efficiency was the aim of the PPV studies. The results presented here elucidated the complex photophysical processes that influence the emission properties of this family of azobenzene-modified PPV derivatives. Important guidelines to maximize modulation efficiency were determined based on these results which will aid researchers in the design of photomodulated conjugated polymers.