Publication Date

5-2022

Advisor(s) - Committee Chair

Matthew Nee, Director, Eric Conte, Jeremy Maddox

Degree Program

Department of Chemistry

Degree Type

Master of Science

Abstract

Monitoring chemical reactions in aqueous solution is a challenge because most instrumental techniques either are not suited for the rapid timescales, are not sensitive enough to detect products at low concentrations, or do not have sufficient structure-to-spectrum relationships. Raman spectroscopy is a promising method to monitor reactions, as it is fast, dependent on chemical structure, and has little interference from water. However, Raman scattering is generally very weak. Surface-enhanced Raman spectroscopy (SERS) improves the signal strength of Raman spectroscopy by using a metal surface plasmon, or oscillation of the surface’s electrons, to allow for highly selective and sensitive detection and characterization of analyte molecules. An aqueous colloid of partially aggregated gold nanoparticles is an accessible substrate for generating plasmons necessary for SERS. The analyte is adsorbed to the nanoparticles, initiating aggregation. A surfactant (sodium dodecyl sulfate) is added at an optimal time to arrest aggregation, leading to a highly stable substrate. Because of this, SERS enhancement is present over multiple hours under powerful UV light. As peaks in the Raman spectra evolve, structural changes can be detected. Paraquat, a common yet dangerous herbicide that is banned in the UK, China, Brazil, and many other countries, was monitored with SERS in real time as it degrades when exposed to intense light, analogous to sunlight. The photodegradation products have not been well characterized in the past, but methylpyridinium is expected. A reaction mechanism and kinetics can then be determined for this reaction. Gathering better data about paraquat and its degradation in the environment may help users apply or sequester paraquat to minimize harm to humans and the ecosystem.

Disciplines

Analytical Chemistry | Chemistry | Materials Chemistry | Physical Chemistry | Physical Sciences and Mathematics

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