Role of mechanochemical milling in FeVO4 synthesis

Single phase, a FeVO4 triclinic crystalline structure was successfully synthesized by annealing the mechanochemically milled xV2O5·(1−x)α-Fe2O3 composites (x=0.5) at 550 °C for 1 h. X-ray powder diffraction (XRD), simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), Mössbauer spectroscopy, scanning electron microscopy (SEM), and optical diffuse reflectance 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-Fe2O3 and V2O5 and substantially decreased their average grain sizes. The Mössbauer spectroscopy studies showed that the spectrum of the mechanochemically milled composites consisted of three sextets and one doublet, indicating the occurrence of V5+-Fe3+ ion substitutions in the corresponding α-Fe2O3 and V2O5 lattices, respectively. The partially V5+-substituted α-Fe2O3 phase and Fe3+-substituted V2O5 could be the important intermediate phases in the production of FeVO4 single phase. The synthesized FeVO4 phase had a slightly distorted nature with an unequal ratio in Fe3+ population in three inequivalent sites. Simultaneous DSC-TGA studies indicated that the synthesized FeVO4 is thermally stable up to 600 °C. SEM images of the formed FeVO4 confirmed the wide particles size distribution range composed of nano-grains. Optical diffuse reflectance spectroscopy studies showed that the synthesized FeVO4 phase had semiconductor properties, with the band gap energy of ~2.44 eV.