Insights into O2 Activation via MnIIIOOH Species on Mn-Rich Biochar

Although metal-rich biochar (M-BC) is widely used in soil remediation and pollution control, the activation mechanism of molecular oxygen (O2) by M-BC still needs to be clarified due to the low metal loading. In this study, we enhanced the manganese content of low-temperature manganese-rich biochar (Mn-BC) by treating it with hydrogen peroxide (H2O2), resulting in the formation of MnBC-Hx (where x represents the volume of H2O2 used in mL). MnBC-H5 was particularly effective in activating O2, leading to the successful degradation of phenol and dyes. Characterizations showed that the MnII in the outer layer of MnC2O4·2H2O nanoparticles evenly dispersed over Mn-BC was oxidized to MnIII by H2O2. This process was accompanied by the removal of coordinated H2O, resulting in the formation of MnIIIC2O4 on MnBC-H5. Under visible light irradiation, MnIII can bind to O2 to form MnIIIOOH species, which facilitates the transfer of charges and generates superoxide radicals (·O2–) that effectively degrade organics. Notably, MnIII of MnBC-H5 remains stable after the organic degradation reaction. This study will not only provide a theoretical basis for developing environmentally friendly biochar-based catalysts but also promote the study of the environmental effects of biochar.