One-Step Hydrothermal Synthesis of Vanadium Dioxide Structures for Thermochromic Glass Applications

Windows are considered the least efficient elements in the building envelope, leading to high cooling and heating costs. Coating the glazed areas not only reduces operational costs but also enhances occupant comfort. In particular, chromogenic coatings with variable thermo-optical properties attracted strong interest from the scientific community. Among the various technologies, thermochromic coatings are the most promising due to their passive temperature-responsive nature. Vanadium Dioxide (VO2) based thermochromic coatings have been candidates for extensive research due to VO2’s reversible semiconductor-metal phase transition from near-infrared transmitting to blocking states. In this article, VO2 structures were synthesized hydrothermally, and the effects of several experimental parameters, including tungsten (W+6) doping level, reaction time and temperature, reductant type, vanadium concentration, and precursor pH, were investigated. The synthesized structures were subsequently ball-milled and spin-coated on glass substrates, and their thermo-optical properties were measured. The results show that a reaction temperature of 280 ℃ for 72 h combined with tungsten-doping are critical to synthesizing VO2 (M/R) structures via a one-step hydrothermal synthesis without annealing. Furthermore, using tartaric acid as a reductant yielded particles with higher crystallinity; however, V6O13 was present. Similarly, a 1% tungsten doping level and doubling the vanadium concentration yielded particles with higher crystallinity while still exhibiting a phase transition temperature of 41 ℃ and a narrow hysteresis of 4 ℃, suitable for window applications. Further work aims to improve the solar modulation ability by overcoating the ground particles with SiO2 shells while enhancing the sensitivity of the films through the inclusion of photothermal nanoparticles.