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

Abstract

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, CO/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.