Insight into the influence of pyrolysis temperature on Fenton-like catalytic performance of magnetic biochar

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The effects of the pyrolysis temperature on the Fenton-like catalytic performance of magnetic biochar remain unclear. In this study, magnetic biochar (SMBC300, SMBC400, SMBC500) was synthesised at various temperature (300 °C, 400 °C and 500 °C) and used for the Fenton-like degradation of metronidazole. The characterisation results demonstrated the similarity of functional groups and the species of iron oxides in three types of magnetic biochar. Moreover, the size distribution of iron oxides in these composites were obviously affected by the pyrolysis temperature. Metronidazole was rapidly and completely degraded by SMBC400 coupled with H2O2, and its kinetic rate constant was approximately 1.86 and 3.04 times higher than those of SMBC300 and SMBC500, respectively. Electron spin resonance and free radical quenching experiments showed that obvious differences in the ability of three types of magnetic biochar can heterogeneously activate H2O2 to generate OH, and that surface-bound OH plays a key role in the degradation of metronidazole. The differences in Fe (II) content among the types of magnetic biochar were the main reason for the differences in catalytic performance. The degradation of metronidazole by various species of iron oxides showed that FeO was the key component in the catalytic performance of magnetic biochar. This study confirms that magnetic biochar prepared at 400 °C has the best performance in the Fenton-like degradation of metronidazole.