Heterogeneous activation of Oxone by substituted magnetites Fe3−xMxO4 (Cr, Mn, Co, Ni) for degradation of Acid Orange II at neutral pH

• The Co, Mn, and Ni cations affect the activity of magnetite in Oxone activation.
• The degradation was carried out at neutral pH with or without buffered solution.
• The effect of substitution on the activity was related to structural environment.
• The dominant reactive radicals in Oxone activation were SO4− rather than OH.

In this study, the effect of incorporation of transition metals (i.e., Co, Mn, Cr, and Ni) into the magnetite on the reactivity towards Oxone activation was investigated at neutral pH. The magnetite samples were characterized by XRD and EXAFS. Co, Cr, and Ni were in the valences of +2, +3, and +2, respectively, while Mn was in the valences of +2 and +3. These cations occupied the octahedral sites of magnetite, but the distribution of Mn and Ni on the octahedral sites of magnetite surface increased with an increase of substitution extent. The activity of magnetites in Oxone activation was investigated through Acid Orange II (AOII) degradation at an initial pH of 7.0 with or without phosphate-buffered solution. In neutral medium, the AOII degradation by Mn, Cr, and Ni substituting magnetites followed pseudo-first-order kinetics. The incorporation of Co, Mn, and Ni improved the catalytic activity of magnetite in the order Mn < Ni < Co, while Cr showed an inert effect. The dominant reactive radicals were indicated through the scavenging effect of ethanol and tert-butyl alcohols. The different effects of studied substitutions on the reactivity of magnetite were discussed in views of reactive radical species and microstructural environment.

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