Abstract
TiO
2
photocatalysis and ultrasound are emerging technologies for the mineralization of pollutants in water. To further investigate these technologies and to assess whether advantages and synergy can be expected from their differences, phenyltrifluoromethylketone (PTMK) was selected as a test compound for pollutants generating CF
3
COOH, an undesirable final product. The PTMK first-order removal rate constant
k
was
ca
. 14 times higher when the ultrasound frequency was 515 kHz instead of 30 kHz for the same energy, and
ca
. 2.5 times higher when a TiO
2
sample we synthesized was used instead of TiO
2
Degussa P25. On simultaneous photocatalytic and ultrasonic treatment an increase in
k
by a factor between 1.4 and 1.9, depending on the TiO
2
sample, was observed at 30 kHz but not at 515 kHz. On the basis of catalase enzymatic effect upon
k
, these observations are tentatively explained by a photocatalytic OH
*
radical production from sonochemically formed H
2
O
2
, provided that the H
2
O
2
residence time on TiO
2
is sufficient. PTMK ultrasonic pyrolysis was demonstrated by product analysis. The amount of CF
3
COOH was
ca
. 8 times lower in sonicated solutions than in UV-irradiated TiO
2
suspensions, for both frequencies and both TiO
2
samples. Therefore, because of a higher
k
value, a high frequency ultrasonic (pre)treatment is preferable to minimize CF
3
COOH formation.