A facile process to prepare one dimension VO2 nanostructures with superior metal-semiconductor transition

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 degrees C to 200 degrees C, the nanobelts become homogenous and regular. The regular nanobelts are also obtained by the decrease of V2O5 concentration. Samples prepared at 200 degrees 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 degrees C over 48 h and 180 degrees C over 48 h can be transformed into VO2 (M) at 450 degrees C over 2 h, while samples obtained at 200 degrees C over 48 h should be annealed at 500 degrees C for 2 h. The nanobelts are transformed into irregular nanostructures, nanorods and nanobelts at the hydrothermal temperatures of 160 degrees C, 180 degrees C and 200 degrees C, respectively. However, samples prepared at 200 degrees 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 degrees C and the phase transition temperature can be reduced to 58 degrees 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