Promoted catalytic transformation of polycyclic aromatic hydrocarbons by MnO2 polymorphs: Synergistic effects of Mn3+ and oxygen vacancies

Manganese oxide (MnO2) plays an important role in the transformation of organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), in environmental compartments. In this study, various MnO2 polymorphs were prepared, and their catalytic activities were evaluated using anthracene (ANT) as a model molecule without light irradiation. Among the obtained MnO2 materials, amorphous MnO2 exhibited the highest catalytic activity to degrade ANT. The reaction rate constant (kobs) positively correlated with the content of Mn3+ in the MnO2 catalysts. Moreover, the production of Mn3+ enhanced the concentration of oxygen vacancies which were conducive to the adsorption of O2 by MnO2, leading to an enhanced level of superoxide radicals O2− generated on the MnO2 surface. MnO2-mediated degradation of ANT was a combination of non-radical oxidation by Mn3+ and radical-based degradation by O2−. These findings provided valuable insights into the environmental fate of PAHs and the potential application of MnO2-based materials for PAHs remediation.