Kinetics and mechanism of pentachlorophenol degradation by sonication, ozonation, and sonolytic ozonation

The decomposition of pentachlorophenol (PCP) by sonication was investigated at two frequencies (20 and 500 kHz) and two concentrations (20 and 60 mu M) to gain insight into the kinetics and mechanisms occurring at different frequencies. Results suggest the presence of parallel pyrolysis and OH. reaction pathways that are altered both as a function of frequency and PCP concentration. In addition, ozone was added to the system and compared to experiments of sonication and ozonation separately to explore the mechanism of sonolytic ozonation. The addition of ozone during sonication did not affect the first-order degradation constant for PCP, compared to the linear combination of separate sonication and ozonation experiments; hence; the residual kinetic effect of the combined system was zero (k(US/O3) = 0). Observed byproducts of sonication include the following: tetrachloro-o-benzoquinone (o-chloranil), tetrachlorocatechol (TCC), oxalate,and chloride.