title: Experimental and modeling approach to decolorization of azo dyes by ultrasound: degradation of the hydrazone tautomer.
abstract: Sonochemical bleaching of monoazo dyes C.I. Acid Orange 7 and C.I Acid Orange 8, which exist in their hydrazone forms in dye solutions, was investigated by irradiating 40 microM dye solutions using a 300 kHz emitter. It was found that the rate of bleaching was first-order with respect to the maximum absorption of the dye in the visible band and accelerated with increased acidity. Decolorization of Acid Orange 7 was slightly faster than that of Acid Orange 8 at equivalent test conditions. The oxidative degradation of Acid Orange 7 and Acid Orange 8 were modeled by means of density functional theory calculations. The adduct formation by hydroxyl radical attack to the carbon atom bearing the azo linkage was more preferred over the attack on the nitrogen atom. A competing reaction of hydrogen abstraction from the CH3 group in C.I Acid Orange 8 was found responsible for the difference in color removal rates.
authors.affiliation: Department of Chemistry, Boğaziçi University, 34342 Bebek, Istanbul, Turkey.
authors.forename: Alimet Sema
authors.initials: AS
authors.lastname: Ozen
authors.forename: Viktorya
authors.initials: V
authors.lastname: Aviyente
authors.forename: Gökçe
authors.initials: G
authors.lastname: Tezcanli-Güyer
authors.forename: Nilsun H
authors.initials: NH
authors.lastname: Ince
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D003116:Color; D004396:Coloring Agents / Q000737:chemistry*; D003198:Computer Simulation; D006835:Hydrazones / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013057:Spectrum Analysis; D014465:Ultrasonics
chemical_list: D001391:Azo Compounds; D004396:Coloring Agents; D006835:Hydrazones; D017665:Hydroxyl Radical