Singlet oxygen dominated core-shell Co nanoparticle to synergistically degrade methylene blue through efficient activation of peroxymonosulfate

Peroxymonosulfate-based advanced oxidation processes (PMS–based AOPs) catalyzed by cobalt nanoparticles have attracted increasing attention due to their special valence electron structure. In this study, nitrogen-doped carbon-encapsulated Co nanoparticle catalysts with core–shell structure were prepared using a simple pyrolysis method at different pyrolysis temperatures (Co@NC-T, T = 650 °C, 750 °C, 850 °C, and 950 °C). Co@NC-750 exhibited excellent activity and high stability for PMS–based removal of methylene blue (MB). More than 99.9 % of MB was degraded with 20 mg/L Co@NC-750 and 100 mg/L PMS within 10 min, displaying good catalytic performance under a wide pH range (3.0–9.0). The quenching tests and electron spin resonance examination results indicated that nonradical, singlet oxygen ( 1 O 2 ), was the major reactive oxygen species in the Co@NC-750/PMS system, other than the radicals. Density functional theory analysis verified that the Co nanoparticles contained heteroatoms N in the carbon layers and provided outstanding activity in activating PMS, as well as good stability, reusability, and versatile adaptability. The analysis of intermediates also revealed that the MB degradation pathway. The results obtained in this study may help to elucidate the application of cobalt species in nonradical–dominated AOPs and stimulate the development of efficient and stable cobalt-based catalysts.