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Study of influence of organic dye structure on their decomposition in the diaphragm discharge in liquids
Pajurková, Jana ; Fasurová, Naděžda (referee) ; Kozáková, Zdenka (advisor)
The main goal of presented thesis is to study the influence of organic dyes structure on its degradation in diaphragm discharge in liquids. Diaphragm discharge is a kind of non-thermal plasma that can be generated in liquids by the application of high voltage. In plasma channels (so-called streamers), many physical and chemical processes are formed. High electrical field, shock waves and last but not least emission of electromagnetic waves in the range of visible and ultra-violet radiation appear among physical processes. The most important chemical process is generation of active species. These species initiate chemical reactions and could attack molecules of organic compounds contained in water solution. The reason why organic dyes were chosen in this study is its visible destruction, because it is related to its decolouration. Further, UV-VIS spectroscopy for the determination of concentration during the experiment can be used. Organic dyes are good models of organic substance often contained in waste water and for which removal classical biological, chemical and physical methods aren’t sufficient. Selected dyes were mostly from the group of azo-dyes: Acid Red 14, Acid Red 18, Acid Yellow 23, Direct Blue 53, Direct Red 79, Direct Red 80, Direct Yellow 29, Food Yellow 3 and further, Acid Blue 74 (indigotic dye) and Direct Blue 106 (oxazine dye). Experiments were carried out in a special batch discharge reactor with the anode and the cathode spaces divided by a non-conductive barrier, where the diaphragm with a pin-hole was placed. Measurement showed different removal in the anode and cathode space. We have supposed it was caused by different streamers features and energetic conditions. Dyes were decomposed with higher efficiency in the anode space where the final concentration reached 40 % of the initial concentration while it remained about 90 % in the cathode space. In this thesis the influence of dyes structure on the dye decomposition by electrical discharge was investigated. Dyes consisted of small molecules and dyes with many substitutes bounded on aromatic ring were decomposed more easily than dyes consisted of big molecules. The shift of characteristic wavelength on both directions (to shorter as well as longer wavelength) was observed during the experiments especially when the Direct dyes were decomposed. This phenomenon was probably due to the formation of intermediate product, which have different characteristic wavelength than the primary compound. In general, colourfulness is given by long conjugated systems of double bonds with substitutes bounded on an aromatic ring. Each change in the molecule structure provides the colour change and this could be the possible reason of the shift of characteristic wavelength. The other task was the comparison of degradation process efficiency by the mean of electrolysis and diaphragm discharge. Results showed that electrolysis (30 W) was more convenient for degradation of dyes consisted of small molecules while diaphragm discharge (130170 W) suited for complex molecules. For degradation of small molecules, oxidation on the anode assumed to be the most effective process that is initiated by electrolysis. For degradation of big molecules, attack of active species produced by the discharge is necessary.
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Study of influence of organic dye structure on their decomposition in the diaphragm discharge in liquids
Pajurková, Jana ; Fasurová, Naděžda (referee) ; Kozáková, Zdenka (advisor)
The main goal of presented thesis is to study the influence of organic dyes structure on its degradation in diaphragm discharge in liquids. Diaphragm discharge is a kind of non-thermal plasma that can be generated in liquids by the application of high voltage. In plasma channels (so-called streamers), many physical and chemical processes are formed. High electrical field, shock waves and last but not least emission of electromagnetic waves in the range of visible and ultra-violet radiation appear among physical processes. The most important chemical process is generation of active species. These species initiate chemical reactions and could attack molecules of organic compounds contained in water solution. The reason why organic dyes were chosen in this study is its visible destruction, because it is related to its decolouration. Further, UV-VIS spectroscopy for the determination of concentration during the experiment can be used. Organic dyes are good models of organic substance often contained in waste water and for which removal classical biological, chemical and physical methods aren’t sufficient. Selected dyes were mostly from the group of azo-dyes: Acid Red 14, Acid Red 18, Acid Yellow 23, Direct Blue 53, Direct Red 79, Direct Red 80, Direct Yellow 29, Food Yellow 3 and further, Acid Blue 74 (indigotic dye) and Direct Blue 106 (oxazine dye). Experiments were carried out in a special batch discharge reactor with the anode and the cathode spaces divided by a non-conductive barrier, where the diaphragm with a pin-hole was placed. Measurement showed different removal in the anode and cathode space. We have supposed it was caused by different streamers features and energetic conditions. Dyes were decomposed with higher efficiency in the anode space where the final concentration reached 40 % of the initial concentration while it remained about 90 % in the cathode space. In this thesis the influence of dyes structure on the dye decomposition by electrical discharge was investigated. Dyes consisted of small molecules and dyes with many substitutes bounded on aromatic ring were decomposed more easily than dyes consisted of big molecules. The shift of characteristic wavelength on both directions (to shorter as well as longer wavelength) was observed during the experiments especially when the Direct dyes were decomposed. This phenomenon was probably due to the formation of intermediate product, which have different characteristic wavelength than the primary compound. In general, colourfulness is given by long conjugated systems of double bonds with substitutes bounded on an aromatic ring. Each change in the molecule structure provides the colour change and this could be the possible reason of the shift of characteristic wavelength. The other task was the comparison of degradation process efficiency by the mean of electrolysis and diaphragm discharge. Results showed that electrolysis (30 W) was more convenient for degradation of dyes consisted of small molecules while diaphragm discharge (130170 W) suited for complex molecules. For degradation of small molecules, oxidation on the anode assumed to be the most effective process that is initiated by electrolysis. For degradation of big molecules, attack of active species produced by the discharge is necessary.
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