Degradation of diclofenac and carbamazepine by the copper(II)-catalyzed dark and photo-assisted Fenton-like systems

Abstract

The oxidative degradation of two pharmaceutical compounds (diclofenac and carbamazepine, denoted as DCF and CBZ) by the Cu(II)-catalyzed Fenton (Cu(II)/H2O2) and the photo-Fenton (UV/Cu(II)/H2O2) systems was examined, with a focus on the parameters that affected the oxidant production, such as the solution pH, the Cu(II) concentration, and the radical scavengers. The degradation of DCF and CBZ in the Cu(II)/H2O2 and UV/Cu(II)/H2O2 systems followed the pseudo-first-order kinetics, which exhibited increasing rate constants with the increasing concentration of Cu(II). In the Cu(II)/H2O2 system, the optimal degradation of the target contaminants was observed at approximately pH 8, which is attributed to the combined effects of two pH-dependent factors: (1) the accelerated Cu(II) reduction by H2O2 with increasing pH and (2) the shift of the main oxidant from the hydroxyl radical (<sup/>OH) to the cupryl ion (Cu[III]) at high pH values. The complete prevention of the degradation of DCF and CBZ in the presence of excess tert-butanol indicates that <sup/>OH is dominantly responsible for the contaminant degradation. The UV-A irradiation significantly enhanced the degradation of the target contaminants over the entire pH range studied (pH 3-10) and slightly shifted the optimal pH conditions to lower values (pH 6-7). The enhanced degradation of the contaminants by the UV/Cu(II)/H2O2 system appears to result from the accelerated Cu(II) reduction by the hydroperoxyl/superoxide radicals (HO2/O2-), which are produced via the photolysis of H2O2.