Cobalt doped g-C3N4 activated peroxymonosulfate for organic pollutant degradation: Alterations in cobalt species and reactive oxygen species

Cobalt-based materials are promising catalysts for activating peroxymonosulfate (PMS) to degrade organic pollutants. Among various cobalt-based catalysts, the alteration in cobalt species and the reactive species produced are not fully understood. Herein, four materials were synthesized by controlling synthesis methods and doping of g-C₃N₄ to regulate cobalt species. Through two methods, ZIF/Co and Co₃O₄, whose main cobalt species are Co–O/Co–N and CoO/O–CoO, were synthesized. On this basis, ZIF/Co–CN and Co₃O₄–CN were synthesized by adding g-C₃N₄. Then, the four materials were used to activate PMS for carbamazepine (CBZ) degradation, focusing on the correlation between active sites and reactive species. CoO/O–CoO mainly led to the formation of free radicals, while Co–N tended to produce non-free radicals. The addition of g-C₃N₄ would facilitate non-free radical catalysis by promoting the conversion of Co–O to Co–N and enhancing the catalytic role of C and N. Finally, the systems with a high proportion of non-free radicals showed better degradation performance when multiple pollutants co-existed, and reactive species may be selective to different pollutants. The findings have significance for the synthesis design of cobalt-based catalysts and the regulation of reactive species to degrade different pollutants practically.