Enhancement of sonochemical degradation of phenol using hydrogen atom scavengers.

Sonochemical degradation of phenol was found to be enhanced in the presence of the volatile hydrogen atom scavengers CCl4 and perfluorohexane. The non-volatile hydrogen atom scavenger iodate did not enhance phenol degradation. The first order rate constant for aqueous phenol degradation in separate experiments using different sonochemical probes increased in the presence of 150 microM CCl4 from 0.014 to 0.031 min(-1) (probe 1) and from 0.022 to 0.061 min(-1) (probe 2). In the presence of <1.5 microM C6H14, the first order rate constant increased from 0.014 to 0.032 min(-1) (probe 1). Hydroquinone was the major observed reaction intermediate both in the presence and absence of hydrogen atom scavengers. Hydroquinone yields were substantially higher in the presence of hydrogen atom scavengers, suggesting that hydroxyl radical pathways for phenol degradation were enhanced by the hydrogen atom scavengers. These additives may be useful in improving pollutant degradation efficiency or improving synthetic processes that rely on hydroxyl radical as a key intermediate.