A cobalt single-atom catalyst with ultralow metal loading for activation of peroxymonosulfate to generate singlet oxygen with almost 100% selectivity

Abstract

Singlet oxygen (¹O₂) is an excellent active species for eliminating organic pollutants in single-atom catalyst (SAC) catalyzed peroxymonosulfate (PMS)-based Fenton-like systems. However, it is difficult to achieve high efficiency and selectivity in ¹O₂ generation as a result of the lack of effective SACs. In this work, a Co SAC (Co–N–C) containing highly uniform Co–N₄ active sites with an ultralow-level Co loading of 0.34 wt% is fabricated, delivering boosted performance in tetracycline degradation with an extremely rapid rate of 0.573 min, which outperforms most advanced catalysts in reported studies. A vibrating-sample magnetometer is used to preliminarily determine the atomically dispersed Co sites in Co–N–C according to the obvious paramagnetic characteristics of Co–N–C, and this is in good agreement with the test results obtained by using an aberration-corrected high-angle annular dark-field scanning transmission electron microscope and synchrotron radiation facility. Electron spin resonance and free radical quenching experiments prove that Co–N–C facilitates PMS activation with the ¹O₂ generation of almost 100%. Mechanism analyses suggest that the Co–N₄ site strengthens the adsorption of the terminal O of PMS, realizing enhanced electron transfer from Co–N–C to PMS, promoting the simultaneous and spontaneous cleavage of O–O and O–H bonds to produce O*, followed by a reaction with another O* to generate ¹O₂.