Unraveling the role of Co(II)-phosphate complex in trace Co(II) activated peroxymonosulfate process for water decontamination with phosphate surrounding

The evolution and role of Co(II)-phosphate complex in pH-dependent peroxymonosulfate (PMS) activation by trace Co(II) for phosphate-contained water decontamination was experimentally and theoretically investigated. The HPO42-species play the most positive effect through forming Co-HPO4 coordination for enhancing radical generation and pharmaceutical degradation (3.59 times) in neutral condition. The reduction of Co(III) to Co(II) was identified as a proton-coupled electron transfer process. In Co(II)/PMS system without phosphate, the protons from the neighboring H2O coordination will bind with the generated SO4 center dot-, inducing proton poisoning effect and in situ radical quenching. While the HPO42-coordination not only modulates the Co 3d electronic structure to optimize the PMS interaction and charge transfer, but also alters the proton affinity to alleviate the proton poisoning effect, securing the radical generation. This study provides insights into the impacts of back-ground factors on advanced oxidation processes and develops strategies for efficient remediation in real (waste) water matrix.