First Experimental Identification of BiVO₄·0.4H₂O and Its Evolution Mechanism to Final Monoclinic BiVO₄

Abstract

The peculiar crystal structure of monoclinic BiVO4 endows it with fascinating and multifunctional properties for potential applications in a wide variety of areas. Notably, previous studies show that an intermediate product called tetragonal scheelite BiVO4 usually appears in the synthetic process of monoclinic BiVO4, which is contrary to the fact that the tetragonal BiVO4 is a high-temperature phase stable above 255 °C. Herein, we first clarify the intermediate product as BiVO4·0.4H2O instead of tetragonal BiVO4 through combination of thermogravimetric analysis (TGA), variable-temperature X-ray diffraction (XRD), differential scanning calorimetry (DSC), IR spectroscopy, and X-ray photoelectron spectroscopy (XPS) results. Moreover, due to the metastable state of BiVO4·0.4H2O resulting from its lattice distortion, it gradually transforms to the final ellipsoidal monoclinic BiVO4 with the increase of reaction time in our system. Briefly, the present work not only shows prospective signs for studying the formation mechanism of various monoclinic BiVO4 products but also provides an effective strategy for elucidating the structural details of other hydrated compounds.