Degradation of bisphenol a using peroxymonosulfate activated by single-atomic cobalt catalysts: Different reactive species at acidic and alkaline pH

Peroxymonosulfate-assisted advanced oxidation processes (PMS-AOPs) catalyzed by single-atom catalysts have become state-of-the-art technologies for environmental remediation. In this study, Cobalt single-atom catalysts supported by graphitic carbon nitride (SA-CoCN) containing Co-N4 active sites were developed as PMS activators for bisphenol A (BPA) degradation. BPA (10 mg L−1) was completely removed with 0.1 g L−1 SA-CoCN and 0.5 mM PMS, and this process was pH-dependent. Instead of the widely recognized generation of free radicals (SO4·– and ‧OH), high-valent cobalt [Co(IV)] and singlet oxygen (1O2) were the predominant reactive species for pollutant degradation under acidic and alkaline conditions, respectively. The conversion of methyl phenyl sulfoxide (PMSO) to methyl phenyl sulfone (PMSO2), electron paramagnetic resonance tests and radical scavenger experiments were used to probe these reactive species. According to density functional theory calculations, the formation of Co(IV) and 1O2 was thermodynamically favorable, and the generation pathways of Co(IV) and 1O2 were further discussed. This study provides an insight into the single-atom cobalt catalyst/PMS process.