A simple method for Mn residue utilization for efficient peroxymonosulfate activation: enrichment of metal sites and oxygen vacancies <i>via</i> alkali-reduction treatment

Transforming Mn residues into catalysts for activating peroxymonosulfate (PMS) for the degradation of organic pollutants is a promising method that could not only mitigate environmental pollution caused by Mn residues, but could also provide inexpensive catalysts for PMS-based wastewater treatment. Herein, a two-step method involving alkali-reduction treatment is proposed for improving the catalytic activity of Mn residues. The proposed alkali treatment successfully reduced the content of Si from 261.0 mg g^-1 to 80.5 mg g^-1, leading to relatively increased contents of Fe and Mn. Moreover, alkaline NaBH₄ reduction treatment introduced more oxygen vacancies, further enhancing the performance. The sample treated with the two-step method exhibited rhodamine B (RhB) degradation kinetics of 0.034 min^-1, which was 2.43 times higher than that of the control sample. Quenching experiments and electron paramagnetic resonance demonstrated the vital role of ¹O₂ in the degradation of RhB, and the mechanism was investigated. Furthermore, 18 types of degradation intermediates were detected, and the possible degradation pathway for RhB was proposed. Through employing a toxicity estimate software tool, it is indicated that RhB toxicity continuously decreases during RhB degradation. The findings of this work could shed light on the reutilization of Mn residues and the development of inexpensive catalysts for PMS-based wastewater treatment.