Scalable Production of Thermochromic Nb-Doped VO<SUB>2</SUB> Nanomaterials Using Continuous Hydrothermal Flow Synthesis

Abstract

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 °C) and improved optical features (narrow hysteresis loop, 10 °C difference) compared to undoped VO2 nanoparticles synthesised under similar conditions. A reduction in the MST temperature of 3.6°C per at.% Nb incorporated was estimated from these studies.