Preparation of multimetal-doped spinel-type catalysts and their application in ozone degradation of phenol
Spinel-shaped ferrite was synthesized using the hydrothermal method,with various metal ions employed to modify the catalyst through doping at the M site.A total of seven catalysts were prepared and screened for their effectiveness in the catalytic ozonation degradation of phenol.The results indicated that the catalytic efficiency of these seven catalysts in the ozonation process was consistent with the observed trends in Chemical Oxygen Demand(COD)removal.When the mass concentration of phenol was set at 30 mg/L,the catalyst concentration at 1 g/L,and the ozone concentration at 6 mg/L,with a flow rate of 1 L/min and a reaction time of 75 minutes,the catalytic efficiency for phenol ozonation was highest for Mn0.5Cu0.5Fe2O4.The efficiency of the other catalysts,in descending order,was as follows:Mn0.5Co0.5Fe2O4,Ni0.5Cu0.5Fe2O4,Zn0.5Cu0.5Fe2O4,Co0.5Cu0.5Fe2O4,Ni0.5Co0.5Fe2O4,and Zn0.5Co0.5Fe2O4.All these catalysts demonstrated higher catalytic efficiency compared to ozone oxidation alone.Considering cost and safety,the Mn0.5Co0.5Fe2O4 catalyst was selected for subsequent experiments.To further investigate its catalytic performance,single metal catalysts MnFe2O4 and CoFe2O4 were also prepared.Under conditions where the mass concentration of phenol was 30 mg/L,the catalyst concentration was 1 g/L,the ozone concentration was 6 mg/L,the flow rate was 1 L/min,and the reaction time was 75 minutes,the removal rates of COD and phenol reached 90.11％and 89.36％,respectively.Compared to other catalysts under the same conditions,the removal rates of COD achieved by ozone oxidation alone,MnFe2O4,and CoFe2O4 increased by 31.16 percentage points,17.41 percentage points,and 4.31 percentage points,respectively.Similarly,the removal rates of phenol improved by 30.51 percentage points,22.23 percentage points,and 8.13 percentage points,respectively.The catalyst was characterized using several methods,including X-ray Diffraction(XRD)and X-ray Photoelectron Spectroscopy(XPS).The results indicated high purity of the catalyst,a favorable degree of crystallization,and successful loading of manganese(Mn)and cobalt(Co)elements.A catalyst cycling test was performed,demonstrating that the Mn0.5Co0.5Fe2O4 catalyst exhibits excellent catalytic stability and reusability.Quenching experiments were conducted,and Electron Paramagnetic Resonance(EPR)was employed to detect free radicals,confirming the involvement of·OH and 1O2 in the phenol degradation reaction within the system.Based on the experimental results,the formation process of free radicals during the Mn0.5Co0.5Fe2O4-catalyzed ozonation degradation of phenol was inferred.
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