A facile process to prepare one dimension VO2nanostructures with superior metal–semiconductor transition

Abstract

VO₂ nanobelts with metal–semiconductor properties were prepared through low temperature hydrothermal reaction and post annealing. X-Ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), differential scanning calorimetry (DSC) and UV-vis-NIR spectrophotometry were employed to investigate the evolution of structure, morphology and properties of the VO₂ nanobelts. The results illustrate that the pure VO₂ (B) nanobelts can be obtained by hydrothermal reaction. The shape of the nanobelts evolves with hydrothermal temperature, time and reactant concentration. With the increasing of hydrothermal temperature from 160 °C to 200 °C, the nanobelts become homogenous and regular. The regular nanobelts are also obtained by the decrease of V₂O₅ concentration. Samples prepared at 200 °C over 48 h have superior morphology and crystallinity. After annealing, VO₂ (B) can be transformed into VO₂ (M), which is dependent on the hydrothermal conditions. Samples prepared at 160 °C over 48 h and 180 °C over 48 h can be transformed into VO₂ (M) at 450 °C over 2 h, while samples obtained at 200 °C over 48 h should be annealed at 500 °C for 2 h. The nanobelts are transformed into irregular nanostructures, nanorods and nanobelts at the hydrothermal temperatures of 160 °C, 180 °C and 200 °C, respectively. However, samples prepared at 200 °C over 48 h with a V₂O₅ concentration of 0.0125 M can keep the intact nanobelts after annealing. The DSC analysis proves that the VO₂ (M) shows good phase transition behavior around 68 °C and the phase transition temperature can be reduced to 58 °C by 0.5 at% tungsten doping. After mixing the VO₂ (M) with acrylic resin, the visible transmission of the VO₂ composite coating on glass is up to 52.2% and the solar modulation at 2000 nm is up to 31.5%, which means that it is a good candidate for smart windows.