Abstract
Metal species and synthetic method determine the characteristics of spinel ferrite MFe2O4. Herein, a series of MFe2O4 (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 MFe2O4 significantly influenced the catalytic persulfate oxidation of organics. The efficiency of the removal of organics using different MFe2O4 + persulfate systems followed the order of CuFe2O4 > CoFe2O4 > MnFe2O4 > ZnFe2O4. Temperature-programmed oxidation and cyclic voltammetry analyses indicated that M-site metal affected the catalyst reducibility, reversibility of M2+/M3+ 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 MFe2O4 in persulfate solution. Moreover, synthetic methods (sol–gel, solvothermal, and coprecipitation) for MFe2O4 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 CuFe2O4 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 MFe2O4 synthesis and persulfate activation.
Highlights
Advanced oxidation processes (AOPs) that involve highly reactive radicals are powerful treatment techniques for the removal of organics in water, especially for removing highly toxic, persistent, and nonbiodegradable organics (Wang and Wang, 2018; Malvestiti et al, 2019)
X-ray powder diffraction (XRD) patterns presented in Supplementary Figure 1 confirmed the successful synthesis of the ferrite samples
The degradation rate constant (Figures 1B,D) was significantly affected by M-site metal, and the trend was basically consistent with the aforementioned catalytic performance order of MFe2O4
Summary
Advanced oxidation processes (AOPs) that involve highly reactive radicals are powerful treatment techniques for the removal of organics in water, especially for removing highly toxic, persistent, and nonbiodegradable organics (Wang and Wang, 2018; Malvestiti et al, 2019). Iron oxides have been generally used as heterogeneous catalysts because of their low price, abundant reserves, and nontoxicity (Li et al, 2017; Silveira et al, 2018). Their weak catalytic activity limits the efficiency of pollutant removal (Lei et al, 2015). Multimetallic iron-based materials can relieve this problem and render catalytic processes more efficient toward long-term application (Deng et al, 2017; Wacławek et al, 2017). In combination with PS, ZnFe2O4 exhibited good photocatalytic performance in the degradation of Orange II (Cai et al, 2016)
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