Boosting the singlet oxygen production from H₂O₂ activation with highly dispersed Co-N-graphene for pollutant removal

Singlet oxygen (¹O₂) is a promising reactive species for the selective degradation of organic pollutants. However, it is difficult to generate ¹O₂ from H₂O₂ activation with high efficiency and selectivity. In this work, a graphene-supported highly dispersed cobalt catalyst with abundant Co-N active sites (Co-N-graphene) was synthesized for activating H₂O₂. The Co-N-graphene catalyzed H₂O₂ reaction system selectively catalyzed ¹O₂ production associated with the superoxide radical (O₂˙^-) as the critical intermediate, as proven by scavenger experiments, electron spin resonance (ESR) spin trapping and a kinetic solvent isotope effect study. This resulted in excellent degradation efficiency towards the model organic pollutant methylene blue (MB), with an outstanding pseudo-first-order kinetic rate constant of 0.432 min^-1 (g L_catalyst ^-1)^-1 under optimal reaction conditions (C _H = 400 mM, initial pH = 9). Furthermore, this Co-N-graphene catalyst enabled strong synergy with HCO₃ ^- in accelerating MB degradation, whereas the scavenger experiment implied that the synergy herein differed significantly from the current Co²⁺-HCO₃ ^- reaction system, in which contribution of O₂˙^- was only validated with a Co-N-graphene catalyst. Therefore, this work developed a novel catalyst for boosting ¹O₂ production from H₂O₂ activation and will extend the inventory of catalysts for advanced oxidation processes.