A facile pathway to fabricate VO2(M) nanoparticles via sol-gel method for flexible thermochromic films with efficient infrared stealth

Large-scale production of uniformly sized Monoclinic vanadium dioxide (VO2(M)) nanoparticles for the flexible films with efficient thermochromic properties remains a challenge. Herein, we reported a facile, scalable sol-gel method combined with post-annealing to synthesize spherical VO2(M) nanoparticles by controlling the concentration of H2O2 solution, the oxygen intake, annealing time and annealing temperature. Optimized VO2(M) nanoparticles had a particle size of about 64.1 ± 25.4 nm and a phase transition temperature of 72.0 ± 1.2 °C with an accompanying latent heat of 25.52 ± 1.89 J/g. The flexible films containing optimal VO2(M) nanoparticles exhibited excellent thermochromic performances with solar modulation efficiency of 8.9 ± 0.6 % and luminescence transmittance of 56.4 ± 2.3 %, and also showed distinct infrared stealth characteristics. This work demonstrated a promising route to prepare uniform nano-oxides via sol-gel method, and proved that the size decrease of VO2(M) nanoparticles facilitates to the improvement of the flexible films thermochromic properties.