Activation of persulfate by Co3O4 nanoparticles for orange G degradation

Abstract

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.