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Graduation Term

2020

Degree Name

Master of Science (MS)

Department

Department of Chemistry

Committee Chair

Jun-Hyun Kim

Abstract

Scientists are on a continuous quest to discover increasingly efficient optical materials that do not require expensive electrical thermal input; pressing environmental concerns and the high demand for renewable energy call for reasonable, inexpensive, and reliable solutions. Nanoscale metal particles are, in particular, highly attractive optical materials due to their large surface areas, tunable structural changes, and easy recyclability. The optical property (i.e., the strong and tunable absorption property) of metal nanoparticles originates from the surface plasmon resonance (SPR, the collective oscillation of conducting electrons on a metal surface). Upon exposure to light, these nanoparticles can transition to an excited state and the resulting electrons can relax back into their ground state, releasing energy in the form of heat. This heating event allows for a temperature increase on the surface of metal nanoparticles and/or a reaction medium that can be applied to light-enhanced catalytic reactions and surface enhanced Raman spectroscopy (SERS) substrates. Particularly, designing various optically active nanoparticles including anisotropic structures with increased surface areas and controlling their arrangements could bring additional advantages to maximize their interactions with light via interparticle coupling for these applications. For example, the systematic combination of plasmonic metal nanoparticles (AgNPs, AuNPs, Ag core-Au shell NPs, and anisotropic AuNPs) on flexible paper-based materials to induce signal-enhancing environments for SERS applications. The subsequent addition of a second layer with these four NPs (e.g., sandwich arrangement) leads to a notable increase of the SERS signals by inducing a high probability of electromagnetic field environments associated with the interparticle SPR coupling and hot spots. The optimized combination is then employed in the detection of microRNA to demonstrate their practicability as SERS substrates. In addition, anisotropic AuNPs are physically encapsulated within a functional group-free poly(N-isopropylacrylamide) particle to test as quasi-homogeneous photocatalysts in the homocoupling reaction of phenylboronic acid. Optimization of the reaction conditions readily allows for the resulting composite particles to serve as recyclable catalysts with high reactivity and selectivity under a broadband light source. Designing these photocatalysts possessing efficient light-induced properties can potentially allow the development of optically active photocatalysts that can harvest broadband light and subsequently release energy in the form of heat in green catalytic reaction systems. The main goal of this research is the investigation of various structure-dependent optical properties to understand their roles in model catalytic reactions and SERS.

Access Type

Thesis-ISU Access Only

DOI

http://doi.org/10.30707/ETD2020.Lartey.J

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