Catalytic degradation of diclofenac by ZnO-Co3O4: identification of major intermediates and degradation pathway

Abstract

ZnO-Co₃O₄ material was successfully synthesized by the co-precipitation method and used as a catalyst for the removal of diclofenac sodium (DCF). ZnO-Co₃O₄ exhibited higher catalytic activity in the catalytic process compared to the photocatalytic processes. Under optimum conditions, the activation of peroxymonosulfate (PMS) by ZnO-Co₃O₄ 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-Co₃O₄/PMS system are singlet oxygen (¹O₂) and superoxide radicals (O₂^•−). The activation of PMS by ZnO-Co₃O₄ was associated with the coexistence and interaction between Co(II) and Co(III), as well as the formation of oxygen vacancies (V₀) 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-Co₃O₄/PMS system is a promising catalytic process for the degradation of organic molecules.