Aquatic photodegradation of clofibric acid under simulated sunlight irradiation: kinetics and mechanism analysis

Clofibric acid is one of the most frequently detected pharmaceuticals in various aquatic environments. Photodegradation of clofibric acid in water under simulated sunlight was investigated. The effects of different initial concentrations, pH conditions and dissolved oxygen were examined. Photodegradation of clofibric acid followed a pseudo-first-order kinetics model, and the rate decreased gradually with the increasing initial concentration of clofibric acid. Dissolved oxygen inhibited the photodegradation of clofibric acid. As a result of varying reaction species of clofibric acid, the initial pH conditions greatly influenced its photodegradation. Quenching experiments showed that the self-sensitization process via ·OH and 1O2 occured during photodegradation of clofibric acid, and the bimolecular reaction rate constants of clofibric acid with ·OH and 1O2 were determined via the competition kinetics method to be 3.93(±0.20) × 108 and 2.38(±0.12) × 106 L mol−1 s−1, respectively. In addition, the transformation products of clofibric acid were identified by the UPLC-Q-TOF-MS microsystem, and eight products were detected. It is proposed that the photodegradation of clofibric acid occurred mainly via decarboxylation, dechlorination, ·OH addition and 1O2 attack reaction.