Performance of Dye-Containing Wastewater Treatment Using MnxOy-Catalyzed Persulfate Oxidation

Dye wastewater is characterized by high salinity, intense coloration, difficulty in degradation, and complex organic compositions, posing significant environmental risks. Manganese oxide (MnxOy)-based materials have been widely used for the removal of recalcitrant organic pollutants in water environments. In this study, various MnxOy polymorphs were prepared, and their catalytic activities for persulfate (PS) activation were evaluated using Orange II (AO7) as a model molecule. After 50 min treatment, the degradation efficiency of AO7 ranked as α-MnO2/PS > γ-MnO2/PS > β-MnO2/PS > Mn2O3/PS, with α-MnO2/PS achieving the highest efficiency of 98.6%. XPS, XRD, and electrochemical analyses indicated that α-MnO2 exhibited an exceptional crystal structure and performance. The α-MnO2/PS system exhibited a strong pH adaptability across a wide pH range of 3.0–9.0. The presence of coexisting anions at 0.1 mM, including Cl−, NO3−, CO32−, and SO42−, slightly reduced the degradation rate of AO7. The reactive oxygen species, mainly SO4•− and 1O2, predominantly destroyed the naphthalene ring structure of AO7. Furthermore, α-MnO2 exhibited an excellent stability, allowing for multiple reuse cycles without interference from common anions in water, highlighting its strong potential for practical applications. These results provided insights into the environmental fates of AO7 in the α-MnO2/PS system.