Manganese doped iron–carbon composite for synergistic persulfate activation: Reactivity, stability, and mechanism

Highlights: • Mn–Fe–C composite was tailor-designed to promote catalytic electron transfer. • Oxygen functional groups on catalyst promoted PS activation and RhB degradation. • Redox cycle of Fe³⁺ and Fe²⁺ was accelerated by Mn for electron transfer. • The Mn–Fe–C composite exhibited excellent stability and reusability. The heterogeneous catalytic process has been under development for aqueous pollutant degradation, yet electron transfer efficiency often limits the effectiveness of catalytic reactions. In this study, a novel composite material, manganese doped iron–carbon (Mn–Fe–C), was tailor designed to promote the catalytic electron transfer. The Mn–Fe–C composite, synthesized via a facile carbothermal reduction method, was characterized and evaluated for its performance to activate persulfate (PS) and degrade Rhodamine Blue (RhB) dye under different pH, catalyst dosages, PS dosages, and pollutant concentrations. Electron spin resonance, along with quenching results by ethanol, tert-butanol, phenol, nitrobenzene and benzoquinone, indicated that surface bounded SO₄^{• −} was the main contributor for RhB degradation, while the roles of aqueous SO₄^{• −} and ^• OH were very minor. Through characterization by XRD, XPS and FTIR analysis, it was determined that the electron transfer during activation of PS was accelerated by the oxygen functional groups on catalyst surface and the promoted redox cycle of Fe³⁺ and Fe²⁺ by Mn. Finally, the Mn–Fe–C composite catalyst exhibited an excellent reusability and stability with negligible leached Fe and Mn ions in solutions. Results of this study provide a promising design for heterogeneous catalysts that can effectively activate PS to remove organic pollutants from water at circumneutral pH conditions.