Catalytic Wet Peroxide Oxidation of Anionic Pollutants over Fluorinated Fe3O4 Microspheres at Circumneutral pH Values

Fluorinated Fe3O4 microspheres with 7.1 +/- 1.4 wt% of fluoride (F-Fe3O4-1) were prepared via glycothermal synthesis. Fluorination significantly enhanced the activity of F-Fe3O4-1 in catalytic wet peroxide oxidation of anionic dyes (including orange G (OG) and congo red) at pH similar to 7. However, the promotional effect of fluorination became less obvious for amphoteric rhodamine B and was not observed for cationic methylene blue. After reacting with H2O2 (40 mM) for 2 h at pH 6.5 and 40 degrees C, the decolorization rates of OG (0.1 mM) and the pseudo-first-order rate constant were 96.8% and 0.0284 min(-1) over F-Fe3O4-1 versus 17.6% and 0.0011 min(-1) over unmodified Fe3O4. The effects of reaction parameters (initial H2O2 concentration and pH value and reaction temperature) on OG decolorization with H2O2 over F-Fe3O4-1 were investigated. The reusability of F-Fe3O4-1 was demonstrated by OG decolorization in eight consecutive runs. Fluorination increased the isoelectric point of F-Fe3O4-1 to 8.7 and facilitated the adsorption and degradation of anionic dyes on the surface of F-Fe3O4-1 at pH similar to 7. Scavenging tests and EPR spectra supported that hydroxyl radicals were the main reactive species for the OG decolorization over F-Fe3O4-1.