Manganese oxide catalytic materials for degradation of organic pollutants in advanced oxidation processes: A review

Manganese oxides (MnOx), as a class of transition metal oxides, have gained significant attention as effective catalysts in advanced oxidation processes (AOPs) for the remediation of organic pollutants in aquatic environments. This review provides an in-depth analysis of various MnOx types (MnO2, MnO, and Mn3O4), exploring their distinct crystal structures (alpha-, beta-, gamma-, delta-, and lambda-MnO2), diverse morphologies (1D, 2D, and 3D), a range of synthesis methods (hydrothermal, coprecipitation, and sol-gel), along with different modification techniques (doping and compositing). This review examines the catalytic performance and underlying mechanisms of various MnOx catalysts within typical chemical-based AOPs. By establishing a correlation between the structural and morphological properties of MnOx and their catalytic activities, this review elucidates the mechanisms driving pollutant degradation, including both radical and non-radical pathways. The influence of critical factors (such as pH, temperature, pollutant concentration, coexisting ions, and the presence of natural organic matter) is systematically analyzed to provide insights into optimizing AOPs for real-world applications. In summary, we provide a comprehensive overview of recent advances in MnOx materials and their potential applications in AOPs.