Kinetics and degradation mechanism of clofibric acid and diclofenac in UV photolysis and UV/H2O2 reaction

In this study, we investigated the removal of the selected pharmaceuticals, clofibric acid and diclofenac, using UV photolysis and UV/H2O2 reactions. The degradation of diclofenac during UV photolysis reaction was faster than that of clofibric acid. Diclofenac was mainly removed by photolysis reaction; clofibric acid was more sensitive to OH radical. More effective removals of clofibric acid and diclofenac were observed when H2O2 was added in the UV photolysis reaction. The competition kinetics showed that the second-order rate constant between the OH radical and the pharmaceuticals was 5.57 x 10(9) M-1 s(-1) for clofibric acid and 2.45 x 10(9) M-1 s(-1) for diclofenac, respectively. The major reaction intermediates during the UV photolysis and UV/H2O2 reactions of clofibric acid were 4-chlorophenol and hydroquinone, and these intermediates were degraded as phenol with further reaction.