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Enhancement of dye sonochemical degradation by some inorganic anions present in natural waters

Paper ID Volume ID Publish Year Pages File Format Full-Text
48399 46505 2008 9 PDF Available
Title
Enhancement of dye sonochemical degradation by some inorganic anions present in natural waters
Abstract

The sonochemical degradation rate of the charged substrates Acid Blue 40 (AB40) and methylene blue (MB) is enhanced by scavengers of hydroxyl radicals such as bicarbonate, carbonate, bromide, iodide and (only in the case of AB40) nitrite. No rate variation was observed with chloride, nitrate or sulphate, excluding a mere ionic strength effect. Oxidation of bicarbonate, carbonate, bromide, iodide and nitrite yields the corresponding radicals CO3−, Br2−, I2− and NO2, reactive but less than OH. Degradation enhancement can occur if these radicals are sonochemically formed on the surface of the collapsing cavitation bubbles and undergo there radical–radical recombination at a lesser extent than OH. In this way the radicals would be more available than OH for substrate degradation, both at the bubble surface and in the solution bulk, which could more than compensate for their lower intrinsic reactivity. The varied reactivity toward different substrates of the sonochemically formed radical species could then explain why nitrite inhibits MB degradation while enhancing that of AB40. The sonochemical formation of Br2−, I2− and NO2 can give rise to halogenation and nitration in addition to oxidation processes. In fact bromo-, iodo- and nitrophenols were detected upon sonication of phenol in the presence of the corresponding anions, but only at quite elevated concentration values of nitrite, bromide or iodide (above 10 mM). Formation of harmful halogeno- and nitroderivatives could therefore take place on sonication of some wastewater rather than of typical natural waters.

Keywords
Ultrasound; Sonication; Cavitation; Hazardous by-products; Wastewater
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Enhancement of dye sonochemical degradation by some inorganic anions present in natural waters
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 77, Issues 3–4, 10 January 2008, Pages 308–316
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
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