Catalytic degradation of Rhodamine B through peroxymonosulfate activation by the Co-doped hydroxyapatite

Supported Co-based catalysts have shown attractive prospects for peroxymonosulfate (PMS) activation. In this work, Co-doped hydroxyapatite (H-Co/HAP) composites were prepared by a simple hydrothermal method. The Co content in H-Co/HAP could reach 71.2 mg/g, while the Co leaching rate remained relatively low. By right of the excellent catalytic performance, the as-prepared H-Co/HAP could achieve 99.02% degradation of Rhodamine B (RhB) within 10 min in the presence of 0.5 mM PMS and a first-order kinetic rate constant of 0.876 min^-1. Even after 8 cycles, the RhB degradation efficiency remained at 81.96%. In addition, the effects of vital reaction parameters, including catalyst dosage, PMS dosage, initial pH, humic acid, and coexisting anions, on the catalytic performance in the H-Co/HAP10/PMS system were systematically investigated and discussed. The degradation mechanism of a non-radical (¹O₂) as the dominant active specie and a radical (•O₂^- and SO₄^•-) as the minor active specie was identified through quenching experiments and electron paramagnetic resonance testing. Moreover, possible degradation pathways of RhB were proposed in the H-Co/HAP10/PMS system. Overall, this study offers a meaningful strategy for designing high-content Co-based catalysts to degrade dye molecules in wastewater.