Performance and mechanism of antibiotic removal by MOF-on-MOF-derived cobalt and nitrogen-doped magnetic porous carbon activated PMS

In this work, magnetic porous carbon material doped with cobalt and nitrogen (Co@N-MC) was obtained by pyrolysis of ZIF-67@ZIF-8. Various characterization techniques were used to investigate the material properties and cobalt was found to exist as Co0, Co2+, and Co3+. The efficiency of catalytic activation of peroxymonosulfate (PMS) for tetracycline (TC) degradation was investigated and 91.27 % of TC was degraded within 30 min using 0.2 g/L PMS and 0.04 g/L Co@N-MC. Furthermore, the effect of different factors on TC removal from the Co@N-MC/PMS system was examined and it was found that Co@N-MC maintained good catalytic activity and decent anti-interference ability. Additionally, the free radical quenching, electron paramagnetic resonance (EPR) experiments and linear sweep voltammetry (LSV) tests revealed that Co@N-MC activates PMS mainly through radical pathways (sulfate radical, hydroxyl radical and superoxide radical) and non-radical pathways (singlet oxygen、electron transfer), of which the latter is dominant. An examination of the stability of the material revealed that cobalt leaching (0.308 mg/L) was below the national China Emission standard. Possible TC degradation pathways were also proposed. Biotoxicity of major intermediates and end products was significantly reduced compared to TC. Overall, this study provides a novel approach for the preparation of non-uniform cobalt-based catalysts with high efficiency and low cobalt leaching for the activation of PMS.