Degradation of atrazine in heterogeneous Co3O4 activated peroxymonosulfate oxidation process: Kinetics, mechanisms, and reaction pathways

Herbicide atrazine (ATZ) has caused great environmental concern due to its long-term application in agriculture and persistence nature. This study examined the degradation of ATZ in heterogeneously activated peroxymonosulfate (PMS) oxidation processes, using Co3O4 as the catalyst, finding that high PMS concentrations and near neutral pH (pH 6.0) were beneficial for ATZ degradation. ATZ degradation rate was influenced by functional groups present on the Co3O4 surface at varying pH. Complete removal of 20 μM ATZ was achieved in 15 min, with 2.0 mM PMS and 0.4 g/L Co3O4 at pH 6.0. Minimal cobalt leaching occurred during reaction, shown by a maximum dissolved Co concentration (0.06 mg/L) found at pH 3.0 and decreasing with increasing pH. During the reaction, Co3O4 showed high potential for reusability. Structural properties of the pristine and used Co3O4 catalysts were characterized by scanning electron microscope; X-ray diffraction; and X-ray photoelectron spectroscopy, with no changes observed post-reaction. A total of 7 intermediate products of ATZ were detected by liquid chromatography-tandem mass spectrometry, with quantification of intermediate products allowing the contribution of different pathway for ATZ degradation, to be accessed. Transformation pathways including dealkylation, dechlorination-hydroxylation, and alkylic-oxidation were proposed for catalytic decomposition of ATZ in the Co3O4/PMS system.