Peroxymonosulfate activation with an α-MnO₂/Mn₂O₃/Mn₃O₄ hybrid system: parametric optimization and oxidative...

The present study proposed the synthesis of low-toxicity and eco-friendly spherically shaped manganese oxides (α-MnO₂, Mn₂O₃, and Mn₃O₄) by using the chemical precipitation method. The unique variable oxidation states and different structural diversity of manganese-based materials have a strong effect on fast electron transfer reactions. XRD, SEM, and BET analyses were used to confirm the structure morphology, higher surface area, and excellent porosity. The catalytic activity of as-prepared manganese oxides (MnO_x) was investigated for the rhodamine B (RhB) organic pollutant with peroxymonosulfate (PMS) activation under the condition of control pH. In acidic conditions (pH = 3), complete RhB degradation and 90% total organic carbon (TOC) reduction were attained in 60 min. The effects of operating parameters such as solution pH, PMS loading, catalyst dosage, and dye concentration on RhB removal reduction were also tested. The different oxidation states of MnO_x promote the oxidative-reductive reaction under acidic conditions and enhance the SO₄^•-/^•OH radical formation during the treatment, whereas the higher surface area offers sufficient absorption sites for interaction of the catalyst with pollutants. A scavenger experiment was used to investigate the generation of more reactive species that participate in dye degradation. The effect of inorganic anions on divalent metal ions that genuinely occur in water bodies was also studied. Additionally, separation and mass analysis were used to investigate the RhB dye degradation mechanism at optimum conditions based on the intermediate's identification. Repeatability tests confirmed that MnO_x showed superb catalytic performance on its removal trend.