Studies on Formation Mechanisms of Monodisperse Spherical V₂O₅ Particles

Abstract

Monodisperse, submicron-sized spherical metal oxide particles have been widely investigated due to their importance in many areas of science and technology, e.g., pigments, catalyst, raw materials of advanced ceramics, and opal-based photonic crystals. A number of methods have been developed to prepare them. Among these methods, hydrolysis of metal alkoxide in homogeneous solution is one of the most effective methods to prepare high purity spherical metal oxide particles with narrow size distribution. However, application of this method has been limited to relatively inactive metal alkoxide. Here, we report the synthesis of monodisperse, submicron-sized spherical V₂O₅ particles with narrow size distribution via hydrolysis of vanadium isopropoxide (VO(OiPr)₃) in acetone/pyridine mixture solution under air. The formed particles had almost perfect spherical shape and were nonagglomerated as revealed by transmission electron microscopic observations. Their size could be easily controlled from 200 to 800 nm by changing the concentration of pyridine while keeping narrow size distribution (standard deviation, ca. 7%). Elemental and Fourier Transform Infrared analyses revealed that these particles have a composition of V₂O₅ ·xPy ·yH₂O (x≈0.8, y≈0.9) independent of their size. X-ray diffraction studies revealed that these particles have layered structure similar to that of V₂O₅·nH₂O xerogel with an interlayer spacing of ca. 1.05 nm independent of their size, possibly due to the intercalation of H₂O and pyridine between the V₂O₅ sheets. Since V₂O₅ has been extensively studied as an important material in many areas, e.g., catalysis, lithium ion battery, electrochromic device, sensors and actuators, these monodisperse spherical V₂O₅ particles may be highly appreciated in such areas.