Role of Oxidation State of Vanadium in Vanadium Oxide-Hematite Nanoparticles

摘要

Single phase, a FeVO_4 triclinic crystalline structure was successfully synthesized by annealing the mechanochemically milled xV_2O_5·(1-x)α-Fe_2O_3 composites (x = 0.5) at 550 °C for 1 h. X-ray powder diffraction (XRD) and Mossbauer spectroscopy were combined for a detailed study of the assisting role of the mechanochemical milling process. Mechanochemical milling homogeneously mixed the starting materials of α-Fe_2O_3 and V_2O_5 and substantially decreased their average grain sizes. The partially V~(5+)-substituted α-Fe_2O_3 phase and Fe~(3+)-substituted V_2O_5 could be the important intermediate phases in the production of FeVO_4 single phase. In addition, xV_2O_3·(1-x)α-Fe_2O_3 (x = 0.1, 0.3, 0.5, and 0.7) solid solutions were successfully synthesized by mechanochemical activation of V_2O_3 and α-Fe_2O_3 mixtures. Complete solid solutions exist after 12 h ball-milling time for all studied x values. The synthesized xV_2O_3·(1-x)α-Fe_2O_3 solid solutions with x = 0.5 and 0.7 were mainly paramagnetic at room temperature. The study demonstrates that the transformation pathway is related to the valence state of the metallic specie of the oxide used in connection with hematite.