AI Article Synopsis
- Sonochemical bleaching of monoazo dyes was studied using two model dyes at 30 micromolar concentrations under various pH conditions, revealing that the bleaching rate was influenced by acidity levels.
- The bleaching process followed a first-order reaction with respect to the dye's maximum visible absorption, with increased acidity leading to faster bleaching, while alkaline conditions slowed down the reaction due to competition for hydroxyl radicals.
- The rate of decolorization also depended on the dye's molecular size and the type or position of substituents on the azo bonds, with simpler and smaller dye structures bleaching more rapidly than more complex ones.
Article Abstract
Sonochemical bleaching of monoazo dyes was investigated by irradiating 30 microM solutions of two "aryl-azo-naphthol" type model dyes in acidic, neutral and basic conditions using a 300 kHz emitter. It was found that the rate of bleaching in all cases was first order with respect to the maximum absorption of the dye in the visible band, and accelerated with increased acidity. The inhibition observed at alkaline conditions was attributed to the formation of anionic dye structures and their competition with the dye and its intermediate oxidation products for hydroxyl radicals, which are the major precursors of azo dye oxidation in sonicated water. Decolorization of the dyes was also related to the size of the molecule and the type or position of substituents about azo bonds. Comparison of color decay rates at similar conditions showed that the dye with a simple structure, low molecular mass and one ortho-substituent (hydroxyl) about the azo bond bleached considerably faster than the one having a more complicated structure (higher mass) and an additional o-substituent to the azo bond other than the OH group.
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| http://dx.doi.org/10.1016/j.ultras.2004.01.097 | DOI Listing |
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