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 Co 3 O 4 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 Co 3 O 4 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 Co 3 O 4 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, Co 3 O 4 showed high potential for reusability. Structural properties of the pristine and used Co 3 O 4 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 Co 3 O 4 /PMS system.