Visible light enhanced heterogeneous photo-degradation of Orange II by zinc ferrite (ZnFe2O4) catalyst with the assistance of persulfate

• PS promoted ZnFe2O4 catalyst assisted visible light photocatalysis significantly.
• The quantum yield (Φ) of photodegradation of Orange II at 454 nm was investigated.
• Primary reactive species were identified and the degradation mechanism was elucidated.
• Main intermediates were identified and a plausible degradation pathway was proposed.
• The toxicity of the treated solution was decreased to nearly zero.

Visible (Vis) light (⩾420 nm) response ZnFe2O4 photocatalyst was successfully fabricated via a facile reduction-oxidation method and its catalytic activity was demonstrated by the pronounced Orange II decolorization under Vis/ZnFe2O4/PS (persulfate, S2O82−) process. The reaction kinetics, degradation mechanism, catalyst stability, and mineralization as well as the toxicity, were detailed investigated. On the basis of the effects of radical scavengers, the sulfate radical (SO4−) is regarded as the predominant reactive oxidants for the Orange II decolorization, while the hydroxyl radical (OH) is also involved. A possible pathway is proposed according to the intermediates determined by GC-MS. The ZnFe2O4 catalyst maintained high activity and stability with very low iron and zinc leaching during the repeated experiments. At initial pH 6.0, the total organic carbon (TOC) and chemical oxygen demand (COD) removal efficiencies at 300 min were 50.5% and 78.6%, respectively, using 0.5 g/L ZnFe2O4 dosage, 1.0 g/L persulfate, and a 150 W visible light lamp. Toxicity experiments with activated sludge implied that the toxicity of the treated solution increased at the first stage but then declined as the reaction proceeded.

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