Tunable S doping from Co3O4 to Co9S8 for peroxymonosulfate activation: Distinguished Radical/Nonradical species and generation pathways

[Display omitted] •A series of Co9S8 nanorods with different S doping ratios were prepared from Co3O4 precursor;•Dominantly ROS changed from nonradical to radical one along with S doping;•The concentration of 1O2 was in a good linear relationship with ΔOL;•S2− enhanced the conversion effectiveness of PMS to SO4-. The introduction of non-metal heteroatoms is an effective way to improve the catalytic properties of heterogeneous catalysts to peroxymonosulfate. Unfortunately, the influence of foreign elements on the catalytic process has not been deeply revealed. Herein, we reported a series of Co9S8 nanorods catalysts from Co3O4 precursor with different S doping ratios. S doping effectively enhanced the catalytic properties, and the catalytic process gradually switched from non-radical (1O2) into radical (SO4−) with the increase of S doping ratio. Moreover, quenching experiments, EPR, XPS, and radicals quantification indicated that the concentration of 1O2 exhibited a linear relationship with ΔOL. Indicating that 1O2 was derived from the reaction between PMS and OL. S doping also altered the valency of cobalt. In Co3O4/PMS, ROS was generated through Co3+/Co2+ catalytic circle. However, in Co9S8/PMS, Co3+/Co2+/Co0 were all involved and accounted for the generation of ROS due to the low redox potential of S2-. Our work may provide some new clues and strategies for studying the influence of foreign elements on the catalytic process in PMS-based heterogeneous catalytic system.