Biochar alters the selectivity of MnFe₂O₄-activated periodate process through serving as the electron-transfer...

Constructing green and sustainable advanced oxidation processes (AOPs) for the degradation of organic contaminants is of great importance but still remains big challenge. In this work, an effective AOP (MnFe₂O₄-activated periodate, MnFe₂O₄/PI) was established and investigated for the oxidation of organic contaminants. To avoid the severe aggregation of MnFe₂O₄ nanoparticles, a hybrid MnFe₂O₄-biochar catalyst (MnFe₂O₄-BC) was further synthesized by anchoring MnFe₂O₄ nanoparticles on chemically inert biochar substrate. Intriguingly, MnFe₂O₄-BC/PI exhibited different selectivity towards organic contaminants compared with MnFe₂O₄/PI, revealing that biochar not only served as the substrate, but also directly participated into the oxidation process. Electron-transfer mechanism was comprehensively elucidated to be responsible for the abatement of pollutants in both MnFe₂O₄/PI and MnFe₂O₄-BC/PI. The surface oxygen vacancies (OVs) of MnFe₂O₄ were identified as the active sites for the formation of high potential complexes MnFe₂O₄-PI*, which could directly and indirectly degrade the organic pollutants. For the hybrid MnFe₂O₄-BC catalyst, biochar played multiple roles: (i) substrate, (ii) provided massive adsorption sites, (iii) electron-transfer mediator. The differences in selectivity of MnFe₂O₄/PI and MnFe₂O₄-BC/PI were determined by the adsorption affinity between biochar substrate and organics. Overall, the findings of this study expand the knowledge on the selectivity of PI-triggered AOPs.