Study on the mechanism of catalytic oxidative degradation of oxalic acid by two-dimensional (2D) shaped manganese dioxide

We have successfully synthesized two-dimensional (2D) shaped manganese dioxide (S-MnO₂) with a sparse porous tubular structure by the nano-casting method. In addition, we have also synthesized one-dimensional (1D) shaped manganese dioxide (α-MnO₂, β-MnO₂ and δ-MnO₂). The prepared manganese oxide was applied as a catalyst for the catalytic ozonation degradation of oxalic acid (OA) in an experiment. Then, the characterization of the prepared manganese oxide was carried out in a systematic way. The results showed that S-MnO₂ with larger specific surface area and lower average oxidation state (AOS) was more active, which could improve the electron transfer ability and increase the number of oxygen vacancies or surface hydroxyl groups more. Meanwhile, the mechanism of catalytic ozonation for oxalic acid degradation was elucidated and the reactive radicals generated during the catalytic process were identified as hydroxyl radicals (·OH) and superoxide radicals (·O₂^-). Furthermore, S-MnO₂ showed good stability and reusability with high mineralization (91.6%) and degradation (98.5%) of oxalic acid within 120 min. Overall, the results of the study indicate that the prepared S-MnO₂ is an effective, highly stable and recyclable non-homogeneous catalyst.