Water treatment by TiO2 photocatalysis and/or ultrasound: degradations of phenyltrifluoromethylketone, a trifluoroacetic-acid-forming pollutant, and octan-1-ol, a very hydrophobic pollutant

TiO2 photocatalysis and ultrasound are advanced oxidation processes for wat er treatment. Our study aimed at showing, via the purposely chosen title co mpounds, that these techniques can be complementary. For C6H5COCF3 (PTMK), the photocatalytic removal rate was higher than the ultrasonic (515 kHz) re moval rate in the presence of TiO2 In the dark, whereas it was the opposite for octan-1-ol under the conditions employed. Simultaneous UV and ultrasou nd irradiation of the TiO2 suspension led, for PTMK, to a removal rate abou t equal to the sum of the removal rates observed for separate irradiations, and decreased by a factor of approximately 20% for octan-1-ol as if the ph otocatalytic degradation was suppressed by the dominant distribution of oct an-1-ol to the cavitation bubbles. This distribution was substantiated by t he large detrimental effect of octan-1-ol on the PTMK ultrasonic removal ra te. The concurrent use of both techniques allowed a faster removal of both pollutants in binary mixtures. The amount of CF3COOH from PTMK was approxim ately eight times lower in sonicated, than in UV-irradiated, TiO2 suspensio ns. Several intermediate products showed the occurrence of chemical transfo rmations occurring in and/or on the cavitation bubbles. COD decline and CO2 formation were initially higher for ultrasonic than for photocatalytic tre atment, However, complete mineralization (except for CF3COOH) was achieved more rapidly by photocatalysis and even more rapidly by simultaneous use of both techniques.