HPO42− enhanced catalytic activity of N, S, B, and O-codoped carbon nanosphere-armored Co9S8 nanoparticles for organic pollutants degradation via peroxymonosulfate activation: critical roles of superoxide radical, singlet oxygen and electron transfer

In this study, we report a facile synthesis of a novel N, S, B, and O-codoped carbon nanosphere-armored Co9S8 nanoparticle composite (Co9S8@NSBOC) and its superior activation performance toward peroxymonosulfate (PMS) for methylene blue (MB) and ofloxacin degradation. The effects of various experimental parameters and the general applicability of the catalyst were investigated. Particularly, Co9S8@NSBOC exhibited high catalytic activity in a wide pH range of 3–12 and HPO42− exhibited a synergic catalytic effect with Co9S8@NSBOC in the degradation system. Radical quenching tests, EPR measurements and electrochemical analysis demonstrated that the degradation mechanism of pollutants in the Co9S8@NSBOC/PMS system included both radical and non-radical pathways, in which ·O2−, 1O2 and electron transfer played dominant roles. Co2+, S2−, carbon defects, C=O/C–O–C, pyridinic-N, graphitic-N, BC2O and C–S–C species on Co9S8@NSBOC, all contributed to PMS activation. The degradation pathways of MB and ofloxacin were proposed based on HPLC-MS/MS analysis of their degradation intermediates. This work not only presents a facile and practical synthetic method of cobalt sulfide-coupled multi-heteroatom-doped carbocatalysts, but also provides useful insights into their active sites and activation mechanisms toward PMS activation.