Manganese oxide and derivative-modified materials in advanced oxidation processes: A review of modification enhancement and activation mechanisms

Manganese oxides (MnOx), as low-toxicity and high-abundance catalysts, have been demonstrated to hold great promise for application in advanced oxidation processes (AOPs). However, further application of this material is restricted due to its unsatisfactory oxidant activation efficiency. Fortunately, recently remarkable research on deep activation mechanisms and modification of MnOx have been undertaken to improve its reactivity. Herein, modification enhancement mechanisms of MnOx to efficiently degrade various organic contaminants were discussed and highlighted, including metal doping, coupling with other metal oxides, composite with carbonaceous material, and compounding with other support. The activation mechanisms of different MnOx and derivative-modified material (such as doped MnOx, metal oxide-MnOx hybrids, and MnOx-carbonaceous material hybrids) were summarized in great details, which was specifically categorized into both radical and non-radical pathways. The effects of pH, inorganic ions, and natural organic matter on degradation reactions are also discussed. Finally, future research directions and perspectives are presented to provide a clear interpretation on the MnOx initiated AOPs.