Enhanced activation of persulfate by Fe(III) and catechin without light: Reaction kinetics, parameters and mechanism

Highlights: • The PS activation efficiency was enhanced by Fe(III) and CAT without light. • Fe(II) was formed from transient complexing and reduction of Fe(III) and CAT. • Sulfate radical was the predominant species contributed to NPX degradation. • O₂^{• −} was produced but not reacted with NPX in Fe(III)/CAT/PS system. • NPX was efficiently degraded in neutral pH in Fe(III)/CAT/PS system. An environmental-friendly plant polyphenol, catechin (CAT), was applied in Fe(III) activated persulfate (PS) system for naproxen (NPX) degradation in this research. Reaction kinetics, parameters, NPX degradation products and reaction mechanism were investigated. Combining the results of quenching experiments as well as Electron Spin Resonance (ESR), it was observed that SO₄^{• −} was critical in NPX degradation, and the contribution of HO^• was minor in the Fe(III)/CAT/PS system. O₂^{• −} was generated during the reaction but did not contribute to NPX degradation. SO₄^{• −} and HO^• were produced from the PS activation by Fe(II), which was formed from the transient complexing and reduction process between Fe(III) and CAT. The effects of Fe(III), CAT, PS concentration and pH value on NPX degradation were evaluated. Moreover, the mineralization rate was 20.2%, and the toxicity of the treated solution were lower than the initial solution. Nine possible intermediates were determined when using LC-QTOF-MS to analyze, and three degradation pathways were put ward. The results proved that CAT could accelerate the redox cycle of Fe(III)/Fe(II), consequently to strengthen PS activation without light. It was a promising oxidation technology as it offered an energy-saving and hypo-toxic way for refractory organic pollutants treatment, and it was applicable at a comparatively wide pH range.