Synthesis and characterization of Mo–W co-doped VO 2 (R) nano-powders by the microwave-assisted hydrothermal method

Mo–W co-doped VO2(R) nano-powders were successfully synthesized by reducing V2O5 with oxalic acid via a microwave-assisted hydrothermal method. Pure nano-crystals of VO2(R) powders were obtained by adding a proper amount of urea as precipitant at a relatively low temperature (190°C) and within a short time (3 days). Ammonium molybdate and ammonium tungstate were selected as dopants and their effect was also studied. The as-obtained products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). Mo–W co-doped VO2-waterborne polyurethanes (WPU) was then fabricated with isophorone diisocyanate (IPDI), 2,2-bis(hydroxymethyl) propionic acid (DMPA) and nanosized Mo–W co-doped VO2-poly(ε-caprolactone) (PCL) as the starting materials. Organic–inorganic hybrid coatings are always achieved with adjustable contents of Mo–W co-doped VO2. The hybrid coatings with Mo–W co-doped VO2 loading on the glass substrate were characterized by variable-temperature UV–vis–IR transmittance spectroscopy and exhibited good optical properties and metal–insulator transition (MIT) properties in the infrared area. The results showed that the doping ions had little influence on the morphology of co-doped VO2(R), but they effectively reduced the phase transformation temperature (Tc). The Mo–W co-doped VO2(R) nano-powders showed prominent thermochromic properties with a low phase transformation temperature and highly visible light transmittance.