Synthesis of Spinel Ferrite MFe(2)O(4) (M = Co, Cu, Mn, and Zn) for Persulfate Activation to Remove Aqueous Organics: Effects of M-Site Metal and Synthetic Method

Metal species and synthetic method determine the characteristics of spinel ferrite MFe(2)O(4). Herein, a series of MFe(2)O(4) (M = Co, Cu, Mn, Zn) were synthesized to investigate the effect of M-site metal on persulfate activation for the removal of organics from aqueous solution. Results showed that M-site metal of MFe(2)O(4) significantly influenced the catalytic persulfate oxidation of organics. The efficiency of the removal of organics using different MFe(2)O(4) + persulfate systems followed the order of CuFe(2)O(4) > CoFe(2)O(4) > MnFe(2)O(4) > ZnFe(2)O(4). Temperature-programmed oxidation and cyclic voltammetry analyses indicated that M-site metal affected the catalyst reducibility, reversibility of M(2+)/M(3+) redox couple, and electron transfer, and the strengths of these capacities were consistent with the catalytic performance. Besides, it was found that surface hydroxyl group was not the main factor affecting the reactivity of MFe(2)O(4) in persulfate solution. Moreover, synthetic methods (sol–gel, solvothermal, and coprecipitation) for MFe(2)O(4) were further compared. Characterization showed that sol–gel induced good purity, porous structure, large surface area, and favorable element chemical states for ferrite. Consequently, the as-synthesized CuFe(2)O(4) showed better catalytic performance in the removal of organics (96.8% for acid orange 7 and 62.7% for diclofenac) along with good reusability compared with those obtained by solvothermal and coprecipitation routes. This work provides a deeper understanding of spinel ferrite MFe(2)O(4) synthesis and persulfate activation.