Insight into the degradation of tetracycline hydrochloride by non-radical-dominated peroxymonosulfate activation with hollow shell-core Co@NC: Role of cobalt species

[Display omitted] •Hollow shell-core Co@NC with exposed two different cobalt species (i.e., Co NPs and Co-Nx site) was prepared by on-step thermal conversion of ZIF-8@ZIF-67 precursor.•Cobalt species of Co@NC play a crucial role in the non-radical-dominated PMS activation and TCH degradation.•Co-Nx site could directly adsorb PMS (*PMS) and facilitate PMS decomposition to form 1O2 while Co NPs indirectly accelerate the generation of 1O2via electron transfer.•Good stability and reusability, high environmental robustness and universal adaptability were demonstrated in Co@NC/PMS system. Cobalt species often play a crucial role in the sulfate radical (SO4−) generation during peroxymonosulfate (PMS) activation, but their roles in the formation of non-radical-dominated PMS activation are largely unclear. Here, shell-core hollow Co@NC with exposed two different cobalt species (i.e., Co nanoparticles and Co-Nx site) was prepared and used to activate PMS for tetracycline hydrochloride (TCH) degradation. The experimental results and theoretical calculations showed cobalt species play a crucial role in the 1O2-dominated TCH degradation in which Co-Nx directly served as active sites to adsorb PMS (*PMS) to facilitate PMS decomposition to form SO5−, and thereafter evolved into 1O2 by the rapid self-reaction of SO5−, while Co nanoparticles indirectly promote 1O2 generation via electron transfer due to their excellent conductivity. With exposed cobalt species and unique structure, Co@NC showed a remarkable catalytic activity for TCH degradation, outperforming the synthesized NC, Co-NC, and commercial Co3O4, Fe3O4 and MnO2. Meanwhile, the good stability and reusability, high environmental robustness and universal adaptability of Co@NC were demonstrated. The TCH degradation pathways including aniline ring oxidation, the cleavage of functional groups and ring-opening reactions were also proposed. The improved understanding on the roles of cobalt species in the non-radical-dominated PMS activation may inspire the development of efficient, selective, and robust cobalt-based catalysts.