Magnetic bimetallic Fe, Ce-embedded N-enriched porous biochar for peroxymonosulfate activation in metronidazole degradation: Applications, mechanism insight and toxicity evaluation

Bimetallic Fe- and Ce-embedded N-enriched porous biochar (Fe-Ce@N-BC)   was synthesized   to activate peroxymonosulfate   (PMS) for metronidazole (MNZ)   removal. 97.5% decay of MNZ was achieved within 60 min   in Fe-Ce@N-BC/PMS system.   The kinetic reaction rate constant of the Fe-Ce@N-BC/PMS   system (0.0566 min −1 ) was 10.5   times higher than that of the BC/PMS   system (0.0054 min −1 ). The highly dispersed Fe-Ce oxide nanocrystals serve as PMS activation centers, while the addition of nitrogen source increases the surface area and porosity of biochar, as well as enhances the PMS activation performance. It is noteworthy that   graphitic N   and C O   groups in biochar facilitates the PMS activation via a nonradical pathway and the Fe 2+ /Fe 3+ and Ce 3+ /Ce 4+ participate in the radical pathway.   The presence of anion ions of SO 4 2− can promote the MNZ degradation process, while HCO 3 – and Cl − ions suppress the MNZ removal. The MNZ removal using Fe-Ce@N-BC   in salty media behavior similarly with that in DDI water, while the decreased removal efficiency in real effluent could be mitigated by prolonging the reaction time. Finally, the degradation intermediate products of MNZ were identified and the pathway was proposed according to LC-MS analysis. The relatively low cytotoxicity of the Fe@Ce/N-BC evaluated by animal cell (A375) and toxicity evolution of MNZ intermediate products strongly suggest huge potential of utilization of the catalyst for aquatic environmental remediation.