Highly isolated interlayer Co-N4 fixed by heptazine promotes peroxymonosulfate activation to selectively generate singlet oxygen.

Constructing highly efficient Co-N4 catalysts to activate peroxymonosulfate (PMS) and selectively generate singlet oxygen (1O2) is challenging for the degradation of stubborn pollutants. Herein, the highly dispersed Co ions, benzene, and cyano group co-modified carbon nitride (Co-BCCN) was engineered via a supramolecular self-assembly strategy. The isolated Co sites tended to be fixed by interlayer heptazine units in the formation of Co-N4. The unique interlayer Co-N4 structure could facilitate the PMS activation in the confined space and accelerate the generation of reactive oxygen species (ROS). The introduction of the benzene ring rich in π electrons and the electron-withdrawing cyano group disrupted the uniform charge distribution in the Co-BCCN structure. The accumulation of electrons around individual Co atoms became more pronounced, which was conducive to the adsorption of PMS and the generation of 1O2. For sulfamethoxazole (SMX) purification, the removal efficiency reached nearly 100 % within 2 min, with a high rate constant of 2.3342 min-1. In the Co-BCCN/PMS system, 1O2 served as the predominant ROS. Density functional theory (DFT) calculation confirmed that SO•-5 was the key intermediate for the selective generation of 1O2. The toxicity of wastewater after degradation and the practical application were evaluated by ecotoxicity analysis, plant toxicity, and continuous wastewater treatment experiment. This work provides new insights into the effective PMS activation by non-radical-dominated Co-N4 single-atom catalysts for the degradation of organic contaminants.