Less-toxic, cost-effective, stable, and highly efficient catalysts for sodium sulfite (S(IV)) activation are required to degrade organic pollutants from wastewater. Herein, we report the facile thermal synthesis of Mn 2 O 3 @Mn 5 O 8 that activates S(IV) more efficiently than other Mn and transition-metal oxides. Mn 2 O 3 @Mn 5 O 8 exhibits good performance and long-term stability for eliminating various contaminants from aqueous media, including phenol, bisphenol A, nitrobenzene, 2,4-dichlorophenol, and acetaminophen. Its high performance is attributed to its multivalency, unique architecture, surface hydroxyl groups (–OH), and high surface area. X-ray diffractometry and high-resolution transmission electron microscopy revealed that Mn 2 O 3 @Mn 5 O 8 comprises well-combined cubic Mn 2 O 3 and monoclinic Mn 5 O 8 crystalline structures, whereas electron paramagnetic resonance spectroscopy and scavenging tests showed that SO 5 •− , SO 4 •− , and •OH radicals are generated during S(IV) activation, with SO 3 •− as a precursor. The mixed-valence state provides effective and favorable electron transfer via Mn redox cycling (Mn(II) ↔ Mn(III) ↔ Mn(IV)), improving the S(IV) activation performance and catalytic activity. Mn 2 O 3 @Mn 5 O 8 /S(IV) system shows stable performance in the 3.0–7.0 pH range. Density functional theory calculations confirmed the higher catalytic activity as indicated by high –OH adsorption energy and significant inter-charge transformation. This study provides new insights and strategies for the activation of S(IV) using less-toxic metal oxides as catalysts and broadens the scope of heterogeneous Mn-based catalysts and S(IV) chemistry in real-world applications, particularly for the treatment of wastewater.
The treatment of semi-coking wastewater generated during the semicoke production process has long been a bottleneck restricting the development of the coal chemical industry. The Fenton reaction is recognized as one of the most effective strategies for addressing water pollution; however, the susceptibility to mineralization and poor reusability of highly active catalysts has limited their practical application. Herein, a thermoplastic polyurethane (TPU) doped with oleic acid modified Mn 2 O 3 @Mn 5 O 8 (Mn 2 O 3 @Mn 5 O 8 -OA) composite fiber membrane was prepared via melt-blown spinning and blending using a melt-blown pilot setup. This composite was employed to activate peroxymonosulfate (PMS) for the degradation of semi-coking wastewater, achieving a maximum chemical oxygen demand (COD) removal efficiency of 72.4%. Material characterization confirmed successful catalyst immobilization and enhanced surface properties. Theoretical calculations provided molecular-level insights into the adsorption behavior of phenol and its degradation intermediates. The TPU-based membrane significantly improved catalyst stability and reusability while maintaining high catalytic activity, offering an effective strategy for advanced oxidation processes in complex wastewater treatment.
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