Applications of time-resolved surface-enhanced Raman spectroscopy in electrochemical processes.
Item
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Title
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Applications of time-resolved surface-enhanced Raman spectroscopy in electrochemical processes.
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Identifier
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AAI9304733
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identifier
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9304733
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Creator
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Shi, Chongtie.
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Contributor
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Advisers: Ronald L. Birke | John R. Lombardi
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Date
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1992
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Analytical | Chemistry, Physical
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Abstract
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The protonation, adsorption and electroreduction of several compounds containing aromatic rings, 4-nitrobenzoic acid (PNBA), 4-cyanopyridine(4-CNPY), 4-pyridinecarboxaldehyde (ALPY) and 4-(hydroxymethyl)-pyridine (HMPY), were investigated systematically by surface-enhanced Raman spectroscopy (SERS), cyclic voltammetry (CV) and digital simulation. The time-resolved SERS spectra during electrochemical reactions were measured in the time scale from seconds to microseconds. Electrochemical reactions were initiated by potential sweep and potential step waveforms. Transient spectra corresponding to the short-lived species are obtained for the first time-resolved SERS. Products of the reactions are identified by comparison of authentic compounds with the SERS spectrum. Possible intermediates are discussed according to the proposed possible mechanisms for each reaction. The electrochemical reductions of all of the four compounds studied, give rise to chemical coupling products under our experimental conditions. However, the pathways for the product formation are different. In the reaction of p-nitrobenzoic acid, an azoxy compound is formed by the coupling of two different intermediate products, nitroso and hydroxylamine compounds. An azo compound is produced in the electroreduction of 4-cyanopyridine through a coupling step of the reactant with a one-electron reduction intermediate. The formation of 1,2-bis(4-pyridyl)ethane is due to the direct coupling between two identical one-electron reduced radicals in pyridinecarboxaldehyde and 4(hydroxymethyl)pyridine electro-reductions. In conclusion, this thesis has demonstrated: (1) that the dramatic enhancement of Raman signal from the pretreated electrode surfaces, coupled with multichannel detection technique makes it possible to detect time-resolved SERS in milliseconds, even microseconds, without influence of fluorescence which is quenched by the SERS active surface. This quenching is very attractive since fluorescence is a major interference in resonance Raman measurements. (2) As an in-situ surface probe, SERS, especially time-resolved SERS, is ideal for studying adsorption, orientation, and electrochemical reactions. The power of time-resolved SERS is convincingly shown in the detection of short-lived surface intermediate species which are generated during electrode reactions. The information obtained from time-resolved SERS investigations provides direct evidence for the identification of products and intermediates, which are useful in the study of kinetics and mechanisms of the reactions.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
