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Activation of persulfate by Co₃O₄ nanoparticles for orange G degradation

Zhang, Jing, Chen, Mengyan, Zhu, Liang
RSC advances 2015 v.6 no.1 pp. 758-768
azo dyes, bicarbonates, catalysts, chlorides, cobalt, cobalt oxide, free radicals, hydroxyl radicals, ions, iron, liquid chromatography, manganese, mass spectrometry, nanoparticles, nitrates, pH, potassium, potassium persulfate, sodium, temperature
Nano-Co₃O₄ was prepared by a precipitation method and successfully applied as a heterogeneous catalyst to activate persulfate (PS). The heterogeneous character of PS activation with nano-Co₃O₄ was more pronounced at neutral pH as indicated by the maximum degradation rate of orange G (OG) and the low concentration of dissolved cobalt ions. The increasing dosages of nano-Co₃O₄ and PS, and the higher temperature rapidly promoted the degradation kinetics of OG. Sulfate radicals (SO₄˙⁻) and hydroxyl radicals (·OH) were proved to be the primary oxidative species, although the intensity of DMPO-OH signals were much stronger than that of DMPO-SO₄ due to the fast transformation from DMPO-SO₄ to DMPO-OH. The catalyst presented an acceptable stability through using it in five consecutive runs. The degradation pathways of OG in nano-Co₃O₄/PS process were proposed for the first time based on LC-MS analysis. The effects of Cl⁻, NO₃⁻, HCO₃⁻, Co²⁺, Fe²⁺ and Mn²⁺ ions, which usually co-exist as water matrix chemicals with azo-dyes, on OG removal by nano-Co₃O₄/PS were examined intensively. The reactivity of potassium persulfate (PS), sodium persulfate (NaPS) and potassium peroxymonosulfate (PMS) in the presence of nano-Co₃O₄ followed the order of nano-Co₃O₄/PMS > nano-Co₃O₄/PS > nano-Co₃O₄/NaPS.