Advanced oxidation and adsorptive bubble separation of dyes using MnO₂-coated Fe₃O₄ nanocomposite

In this study, MnO₂-coated Fe₃O₄ nanocomposite (Fe₃O₄@MnO₂) was utilized to decompose H₂O₂ to remove dyes via advanced oxidation processes and adsorptive bubble separation (advanced ABS system). The combination of H₂O₂ and Fe₃O₄@MnO₂ generated bubbles and formed a stable foam layer in the presence of a surfactant; sodium dodecyl sulfate (SDS) or cetyltrimethylammonium chloride (CTAC), separating dye from the solution. On the basis of radical quenching experiments, electron paramagnetic resonance and X-ray photoelectron spectroscopy analyses, it was confirmed that the MnO₂ shell of catalyst was reduced to Mn₂O₃ by H₂O₂, generating radicals and oxygen gas for the removal of dyes. In the advanced ABS system, ∙OH and ¹O₂ were the main radical species and the O₂ concentrations of 0.34 and 0.71 mM were increased in the solution and headspace, respectively. The advanced ABS system demonstrated a high removal efficiency of methylene blue (MB) (99.0%) and the removal rate increased with increasing amounts of components (H₂O₂, catalyst and SDS). Also, the advanced ABS system maintained high removal efficiency of MB at a wide pH range of 3-9. In addition to the anionic surfactant of SDS, CTAC was applied as a cationic surfactant for the advanced ABS of anionic dyes. Lastly, the scale-up system was applied to remediate dye-contaminated river water and industrial wastewater for possible practical applications.