Synthesis of W-doped VO2 nanoparticles via an aqueous ammonia solution route using WO3 and V2O5 powders and fabrication of thermochromic smart-window composites

Abstract Ammonium vanadate (NH 4 VO 3 , NH 4 W x V 1-x O 3 ) precursor nanoparticles were synthesized by dissolving V 2 O 5 and WO 3 powders in aqueous ammonia, followed by precipitation through pH adjustment to 2.5. VO 2 and W-doped VO 2 nanoparticles were obtained by heat treating the precursor powder at 450 °C in H 2 , followed by 600 °C in N 2 (99.9999%). The resulting VO 2 particles ranged in size from sub-tens to 300 nm. These particles were embedded in a transparent urethane resin to fabricate composite films. The composite films prepared using undoped and W-doped VO 2 exhibited thermochromic properties, with approximately 10% difference in transmittance in the infrared region at high and low temperatures. The transition temperature of the undoped VO 2 composite film was 68.1 °C, whereas that of the W-doped VO 2 (W 0.026 V 0.974 O 2 ) composite film was 43.0 °C. The VO 2 nanoparticle in this research is an inexpensive aqueous solution method and can be handled in large quantities. The thermochromic composite films can be easily synthesized by dispersing and embedding the resulting VO 2 nanoparticles in a transparent resin. Furthermore, the vanadium can be recovered by firing the matrix resin of the composites. In summary, this investigation enables to design a VO 2 composite films with high environmental effects and low environmental load.