Catalytic degradation of diclofenac by ZnO-CoO: identification of major intermediates and degradation pathway.

ZnO-CoO material was successfully synthesized by the co-precipitation method and used as a catalyst for the removal of diclofenac sodium (DCF). ZnO-CoO exhibited higher catalytic activity in the catalytic process compared to the photocatalytic processes. Under optimum conditions, the activation of peroxymonosulfate (PMS) by ZnO-CoO achieved approximately 99% removal of DCF, confirming the effective adsorption and activation of PMS. Quenching experiments indicated that the reactive oxygen species (ROS) responsible for the degradation of DCF by the ZnO-CoO/PMS system are singlet oxygen (O) and superoxide radicals (O). The activation of PMS by ZnO-CoO was associated with the coexistence and interaction between Co(II) and Co(III), as well as the formation of oxygen vacancies (V) in ZnO. Cobalt leaching was negligible, and the degradation rate remained constant after four cycles, indicating the excellent stability and reusability of the ZnO-Co₃O₄ catalyst. Additionally, eight degradation products of DCF were identified by LC-ESI-MS, and their toxicity was evaluated using ECOSAR software (version 2.2). In conclusion, the ZnO-CoO/PMS system is a promising catalytic process for the degradation of organic molecules.