Dissertations and Theses @ UNI
Availability
Open Access Thesis
Keywords
Semiconductors--Reactivity; Photocatalysts; Gentian violet;
Abstract
The photodecolorization and the photodegradation of the triphenylmethane dye crystal violet (basic violet 3) adsorbed on four metal oxide catalysts was studied. Crystal violet dissolved in methanol was adsorbed onto the surfaces of an anatase and rutile titanium dioxide mixture, rutile titanium dioxide, zinc oxide, and magnesium oxide, and the solvent was allowed to evaporate. The samples were irradiated using a 1000 W mercury-xenon arc lamp with glass optics as a light source. A wide spectrum and narrow regions of the spectrum were studied to determine their impact on the decolorization and degradation of crystal violet. Diffuse reflectance spectroscopy was used to quantitatively monitor reactions on the surface. Thin-layer chromatography and ultraviolet/visible spectroscopy were used to confirm the diffuse reflectance results. It was determined that the efficiency of photodecolorization of crystal violet on anatase/rutile TiO2 was dependent upon the wavelength of irradiation. By isolating various regions of the spectrum, it was determined that catalyst excitation was more efficient than dye excitation in promoting the photodecolorization of adsorbed crystal violet. Also, in this system, the appearance of a narrow absorption band in the blue region of the spectrum was seen. This phenomenon has been seen in other research done in solution and on the surface of various media but not on a metal oxide surface. Diffuse reflectance spectroscopy was used to monitor the formation and destruction of the blue absorbing species. This species is identified as the crystal violet radical and/or the excited triplet state of crystal violet since both absorb in the blue region of the spectrum. The various metal oxides had different cross-section for decolorization of adsorbed crystal violet when irradiated with the full spectrum of light. Equal surface area was chosen as the basis for comparison of the catalysts and the changes in the 578 nm light-absorbing species were monitored using diffuse reflectance spectroscopy for all the metal oxides. The overall general trend of increased reflectance as irradiation time increased was seen for all the metal oxides. Zinc oxide was the most efficient at promoting decolorization of crystal violet, followed by rutile titanium dioxide and magnesium oxide. The antase/rutile titanium dioxide was least efficient at promoting deco lo rizatio n. The four dyed metal oxides were irradiated for various time intervals and the degradation products ere examined to determine the photodegradation mechanism. Spectrophotometry and TLC were used to monitor the photodegradation products. Sequential demethylation of crystal violet was the main pathway of decomposition on anatase/rutile titanium dioxide, rutile titanium dioxide, and zinc oxide. The shifts in maximum absorbances to shorter wavelengths as irradiation time increased were consistent the production of successive demethylation products. While demethylation of crystal violet adsorbed on magnesium oxide does occur slightly, the majority of the decolorization seen is probably due to acid-base chemistry with the surface hydroxyl groups. The photoexcitation and photodegradation mechanism proposed in this thesis emphasizes excitation of the semiconductor catalysts and charge transfer to the dye as the source of the precursor to the demethylation products. Suggestions for further study are presented.
Year of Submission
1999
Degree Name
Master of Arts
Department
Department of Chemistry
First Advisor
Shoshanna Coon
Second Advisor
Curtiss D. Hanson
Third Advisor
Ira M. Simet
Date Original
1999
Object Description
1 PDF file (78 leaves)
Copyright
©1999 Reygan Mashay Freeney
Language
en
File Format
application/pdf
Recommended Citation
Freeney, Reygan Mashay, "Photodecolorization and Photodegradation of Crystal Violet Adsorbed on Metal Oxide Surfaces" (1999). Dissertations and Theses @ UNI. 2664.
https://scholarworks.uni.edu/etd/2664
Comments
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