The remarkable effect of vanadium doping on the adsorption and catalytic activity of magnetite in the decolorization of methylene blue

In this study, a series of vanadium doped magnetites (Fe3−xVxO4, 0 ≤ x ≤ 0.34) was synthesized by a precipitation–oxidation route and show good adsorption and catalytic activities. Powder X-ray diffraction (PXRD) and Mössbauer spectra analysis of Fe3−xVxO4 confirm the formation of magnetite, while Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy and X-ray absorption fine structure (XAFS) spectra indicate vanadium preferentially occupies the octahedral site. The valency of vanadium in magnetite is mainly +3, as inferred from FTIR and XAFS. Thermal analysis (TG–DSC) shows that the incorporation of vanadium in magnetite structure leads to an increase of superficial hydroxyl groups and a decrease in temperature of phase transformation maghemite–hematite. Vanadium incorporation can promote the adsorption of methylene blue (MB) on Fe3−xVxO4 and degradation of the dye with high degree of decolorization. The improvement of adsorption activity may be related to the increase of superficial hydroxyl. The high catalytic activity is related to the improvement of adsorption activity, the intensification of H2O2 decomposition by vanadium on the magnetite surface to produce OH and the improvement of electron transfer by vanadium to produce a more efficient regeneration of the Fenton active specie Fe2+.