Cobalt leaching inhibition: Transforming coordination polymers into spherical Co3O4@NC catalysts for accelerated tetracycline degradation via enhanced PMS activation

In this study, we synthesized Co-based coordination polymer-derived nitrogen-doped carbon-coated Co3O4 spheres (Co3O4@NC) and yolk-shell Co3O4 spheres (Co3O4-YS) under various atmospheric conditions to explore their efficacy in activating peroxymonosulfate (PMS) for tetracycline (TC) degradation. The Co3O4@NC, featuring a significantly higher specific surface area (268.4 m2/g), exhibited remarkable performance by achieving 90% TC removal in 5 minutes using 0.2 g/L PMS and 0.1 g/L of Co3O4@NC. This reaction rate was 9.2 times higher than that observed with Co3O4-YS. Furthermore, the Co3O4@NC/PMS system demonstrated exceptional stability across a wide pH range, in complex water compositions, and the presence of common coexisting ions. The unique coated structures effectively minimized the leaching of Co ions (below 0.447 mg/L). Additionally, the strong magnetism of Co3O4@NC allows for easy separation under a magnetic field. Mechanistic investigations identified 1O2, ∙OH, O2∙-, and SO4∙- as the principal reactive species. The study also explored potential degradation pathways and toxicity.