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 Co 3 O 4 spheres (Co 3 O 4 @NC) and yolk-shell Co 3 O 4 spheres (Co 3 O 4 -YS) under various atmospheric conditions to explore their efficacy in activating peroxymonosulfate (PMS) for tetracycline (TC) degradation. The Co 3 O 4 @NC, featuring a significantly higher specific surface area (268.4 m 2 /g), exhibited remarkable performance by achieving 90% TC removal in 5 minutes using 0.2 g/L PMS and 0.1 g/L of Co 3 O 4 @NC. This reaction rate was 9.2 times higher than that observed with Co 3 O 4 -YS. Furthermore, the Co 3 O 4 @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 Co 3 O 4 @NC allows for easy separation under a magnetic field. Mechanistic investigations identified 1 O 2 , ∙OH, O 2 ∙ - , and SO 4 ∙ - as the principal reactive species. The study also explored potential degradation pathways and toxicity.