Surface dual redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) for heterogeneous peroxymonosulfate activation to degrade diclofenac: Performance, mechanism and toxicity assessment

Highlights: • Mn₃O₄/CuBi₂O₄ with dual redox cycles of Mn³⁺/Mn⁴⁺ and Cu⁺/Cu²⁺ was synthesized. • Advanced oxidation process of PMS activation by Mn₃O₄/CuBi₂O₄ was built. • Highly efficient degradation and toxicity decline of diclofenac were achieved. • Mechanism of dual redox cycles of Mn³⁺/Mn⁴⁺ and Cu⁺/Cu²⁺ to activate PMS was proposed. Advanced oxidation processes (AOPs) based on heterogeneous catalytic activated peroxymonosulfate (PMS) have been becoming alternatives to conventional wastewater treatment technologies to directly degrade chemical contaminants. To build dual/multi redox cycles of different metal ions may be an effective means for better PMS activation. Herein, this study designed Mn₃O₄/CuBi₂O₄ with dual redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) to activate PMS for efficiently decomposing and mineralizing diclofenac sodium (DCF). Under optimal reaction conditions, DCF (50 mg/L) was degraded totally within 10 min, and TOC removal rate reached up to 74.3%. The possible mechanism of PMS activation by Mn₃O₄/CuBi₂O₄ was proposed, wherein dual redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) on Mn₃O₄/CuBi₂O₄ effectively facilitated PMS activation to generate ·O₂⁻, ¹O₂, SO₄·⁻ and ·OH, which was responsible for DCF degradation. Moreover, combined with degraded products detected by high resolution liquid chromatography coupled to mass spectrometry and corresponding toxic assessment results, the possible degradation pathways of DCF were proposed and the relative toxicity of degraded products was evaluated. This work may be useful for developing stronger heterogeneous activators of PMS to construct more efficient AOPs for purifying wastewater.