Manganese Ferrite Supported on Activated Alumina Beads for Activation of Periodate Towards Efficient Degradation of Organic Dye Pollutants

Manganese ferrite (MnFe₂O₄) supported on activated alumina beads (MFO-AABs) was synthesized by solvothermal method and used to activate periodate (PI) to degrade crystal violet (CV) and other organic dye pollutants. Under the optimum conditions (MFO-AABs dosage of 10 beads and PI dosage of 0.4 g/L), the removal efficiency of 10 mg/L CV reached 98.3% in 120 min. This surpassed the sum of removal efficiencies when MFO-AABs and PI presented respectively, indicating that MFO-AABs and PI worked synergistically. The removal efficiency of CV was almost unaffected in the presence of SO₄²⁻(aq.) while slightly inhibited by Cl⁻(aq.), HCO₃⁻(aq.) or HPO₄²⁻(aq.). The effect of initial pH was studied in the range of 3–9, showing that the removal performance of CV was better under acidic and neutral conditions. Reusability tests showed that the removal efficiency of CV declined slightly after MFO-AABs was reused for 4 times, which was attributed to the accumulation of degradation products on the catalyst. Through calcination to remove these adsorbed degradation products, the catalytic ability could be recovered. Quenching experiments showed that ¹O₂ played a major role in the reaction process. The contribution of non-radical electron transfer was ruled out by a series of electrochemical tests. In addition, IO₄⁻(aq.) was stoichiometrically converted to IO₃⁻(aq.) without producing potentially toxic iodine species such as I⁻(aq.), I₂/I₃⁻(aq.) and HOI. Combining liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT) calculations, the possible degradation pathway of CV was proposed with 12 degradation products. Finally, the analysis of potential toxicity was carried out by theoretical calculations as well as experiments with Vigna radiata, revealing the decreased potential toxicity after the degradation process.

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