Dissertations and Theses @ UNI

Award Winner

Recipient of the 2001 Outstanding Master's Thesis Award - Second Place.

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Open Access Thesis

Keywords

Gentian violet--Oxidation; Photodegradation;

Abstract

Photodecomposition and photodecolorization of crystal violet dye were studied in water solution, hydrogen peroxide solution and suspensions of metal oxides. Spectroscopic evidence for the formation of methylated pararosanilines and demethylated derivatives of Michler's ketone as the reaction intermediates was obtained for the photodecomposition of crystal violet in water solution. The mechanism of formation of the intermediates was discussed in terms of charges of individual atoms calculated using Spartan software.

Photooxidation of crystal violet was shown to occur faster in hydrogen peroxide solution due to the higher oxidation potential of hydrogen peroxide and hydroxyl radicals. A mechanism similar to photooxidation in water solution was proposed since the formation of the same intermediates was observed.

The semiconducting oxides Ti02 and ZnO were shown to be more efficient in crystal violet photodecomposition than any of the insulating oxides studied: SiO2, Al2O3, and MgO. Adsorption and wavelength dependent studies of titanium dioxide suspensions are consistent with a pathway in which a dye is oxidized by the surface-bound hydroxyl radicals formed by injection of an electron from adsorbed hydroxyl groups to photogenerated holes. Photogenerated electrons are subsequently scavenged by molecular oxygen to form O2- radical anions and ultimately hydroxyl radicals that can also oxidize the dye. Intermediates/products of photodecomposition were found to be adsorbed on the titanium dioxide surface, which could lower the catalytic efficiency of titanium dioxide as the reaction proceeds. Zinc oxide was found to be the most efficient oxide for crystal violet photodecomposition, but its low photochemical stability makes it unsuitable for industrial catalysis. Photochemically inert oxides were shown to influence the rate of crystal violet photodecomposition. Acceleration of photodecomposition in the presence of aluminum oxide can be explained by stabilization of the excited state of the dye by the aluminum oxide surface, and inhibition of photodecomposition in the presence of silicon dioxide can be explained by the formation of dye clusters on the silicon dioxide surface. Fast decolorization in magnesium oxide suspensions is due to the reaction of crystal violet with hydroxide ion to form a carbinol base. Titanium dioxide was concluded to be the best prospective catalyst for crystal violet photodecomposition of those studied, since it is highly efficient, relatively cheap and chemically stable.

Year of Submission

2000

Year of Award

2001 Award

Department

Department of Chemistry and Biochemistry

First Advisor

Shoshanna Coon, Chair, Thesis Committee

Comments

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Date Original

7-2000

Object Description

1 PDF file (ix, 45 pages)

Language

en

File Format

application/pdf

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