Mechanism of catalytic ozonation for elimination of methyldopa with Fe₃ O₄ @SiO₂ @CeO₂ catalyst

In this study, a magnetic nanocatalyst (Fe₃ O₄ @SiO₂ @CeO₂ ) was prepared and applied in the catalytic ozonation of methyldopa (MD). The effects of operational parameters on catalytic ozonation performance were investigated, including ozone dosage, catalyst dosage, initial MD concentration, and pH. The removal of MD was 45.2% in ozonation, whereas the efficiency was achieved to 83.0% with the addition of Fe₃ O₄ @SiO₂ @CeO₂ . The results showed that Fe₃ O₄ @SiO₂ @CeO₂ could significantly improve the catalytic ozonation performance. And the enhanced mechanism study showed that it was attributed to promotion of ozone decomposition to generate hydroxyl radical. The reaction model was explored, and the reaction rates were calculated for the MD degradation in catalytic ozonation. A higher degradation efficiency of MD in catalytic ozonation was attributed to the enhanced surface effect of the catalysts, which was confirmed by using TBA, PO₄ ^3- , and p-BQ as scavengers of hydroxyl radical, surface reaction, and superoxide radical. The hydroxyl radical and superoxide radical played an important role in the degradation of MD. The mechanism of catalytic ozonation by Fe₃ O₄ @SiO₂ @CeO₂ was discussed via X-ray photoelectron spectroscopy (XPS) spectra and experimental data.