Degradation of aryl-azo-naphthol dyes by ultrasound, ozone and their combination: Effect of α-substituents

• Published in: Ultrasonics sonochemistry Vol. 13; no. 3; pp. 208 - 214
• Main Authors: Gültekin, I., Ince, N.H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-04-2006; Elsevier
• Subjects: Aryl-azo-naphthol; Azo Compounds - analysis; Azo Compounds - chemistry; Chemistry; Chromophore; Coloring Agents - analysis; Coloring Agents - chemistry; Electrophilic; Exact sciences and technology; General and physical chemistry; Hydroxyl radical; Intramolecular hydrogen bonding; Isomerism; Mineralization; Molecular Structure; Naphthols - analysis; Naphthols - chemistry; Oxidation-Reduction; Ozonation; Ozone - chemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Sonolysis; Ultrasonic chemistry; Ultrasonics; Water Pollutants, Chemical - analysis; Water Purification - instrumentation; Water Purification - methods; α -substituent; Aryl-azo-naphthol; Intramolecular hydrogen bonding; Mineralization; Sonolysis; Electrophilic; Ozonation; α -substituent; Hydroxyl radical; Chromophore; Substituent effect; α-substituent; Sonochemistry; Hydrogen; Ozone; Condensed benzenic compound; Degradation; Azo dye; Naphthol derivatives; Aryl; Ultrasound; Hydroxyl
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2005.03.002

Lab-scale degradation of azo dyes with ultrasound (300
kHz), ozone and both was investigated using an aryl-azo-naphthol dye-C.I. Acid Orange 8. It was found that in all schemes color decay was faster than UV absorbance, and the rates followed pseudo-first-order kinetics except for the decay of UV-254 band by ozone. Sonication alone was sufficient for decolorization, but not for UV absorption abatement or mineralization. Ozonation was more effective than ultrasound in bleaching, but not as much for the mineralization of the dye. Combined operation of ultrasound and ozone improved the rate of bleaching and UV absorption decay and remarkably enhanced the mineralization of the dye. This was attributed to increased mass transfer of ozone in solution and its decomposition in the gas phase to yield hydroxyl radicals and other oxidative species. The effect of α-methyl substituent at the aryl carbon of the dye was found to decelerate the rate of degradation as a result of weakened intramolecular hydrogen bonding.