Scalable Production of Thermochromic Nb-Doped VO2 Nanomaterials Using Continuous Hydrothermal Flow Synthesis

The synthesis of effective thermochromic Nb-doped VO2 nanoparticles, containing a range of Nb dopant concentrations (1, 5 and 15 at.% Nb), was carried out via continuous hydrothermal flow process under supercritical water regime. The synthesis method employed here is directly scalable for industrial purposes and the materials may be produced at a rate of kg h(-1) in our pilot plant. The thermochromic properties of these materials were studied at variable temperature using UV/Vis spectroscopy. The structure, morphology and particle properties were characterised using powder X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The incorporation of Nb dopant into VO2 was studied X-ray photoelectron spectroscopy. The Nb-doped VO2 materials showed a substantial decrease in metal-to-semiconductor transition temperature (ca. 20 degrees C) and improved optical features (narrow hysteresis loop, 10 degrees C difference) compared to undoped VO2 nanoparticles synthesised under similar conditions. A reduction in the MST temperature of 3.6 degrees C per at.% Nb incorporated was estimated from these studies.