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Effects of dissolved gas species on ultrasonic degradation of (4-chloro-2-methylphenoxy) acetic acid (MCPA) in aqueous solution.

Kojima Y, Fujita T, Ona EP, Matsuda H, Koda S, Tanahashi N, Asakura Y

Research Center for Advanced Waste and Emission Management, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. ykojima@rescwe.nagoya-u.ac.jp <ykojima@rescwe.nagoya-u.ac.jp>

Sonochemical degradation of MCPA ((4-chloro-2-methylphenoxy) acetic acid) in dilute aqueous solutions was studied using ultrasound with a frequency of 500 kHz. The effect of gas atmosphere on MCPA degradation was investigated in nitrogen (N(2)), air (O(2)/N(2)), oxygen (O(2)), argon (Ar) and Ar/O(2) (60/40% v/v) atmospheres. For sonochemical degradation of MCPA in N(2), air (O(2)/N(2)), O(2) and Ar atmospheres, the rate enhancement of MCPA decomposition by sonolysis was found to be more effective in an O(2)-enriched atmosphere compared to Ar atmosphere. It was considered that a higher amount of oxidants was formed in a higher O(2) partial pressure, which accelerated MCPA decomposition in a radical reaction system. On the other hand, both dechlorination and total organic carbon (TOC) removal rates were higher in Ar atmosphere, compared to those in O(2)/N(2) atmosphere. It was found that, MCPA was most effectively decomposed by sonication in Ar/O(2) (60/40% v/v) atmosphere, with higher rates of decomposition, dechlorination and TOC removal.

Published 13 December 2004 in Ultrason Sonochem, 12(5): 359-65.
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