Self-assembly and synthesis mechanism of vanadium dioxide hollow microspheres

Rutile vanadium dioxide (VO2 (R)) hollow spheres with nanorods aggregating on their surface were successfully synthesized through a novel surfactant-assisted hydrothermal process in which polyvinylpyrrolidone (PVP) served as a soft template. The crystal structure and morphology were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Hollow spheres show an obvious Mott phase transition at 63.0 (heating semicycle) and 53.1 degrees C (cooling semicycle). Reaction conditions influencing the synthesis of these VO2 hollow spherical structures (i.e., reaction temperature, time and PVP addition amount) were investigated. Furthermore, a mechanism for the growth of the VO2 hollow spheres is proposed.