3D mesoporous structure assembled from monoclinic M-phase VO 2 nanoflakes with enhanced thermochromic performance.

Monoclinic M-phase VO 2 is a promising candidate for thermochromic materials due to its abrupt change in the near infrared (NIR) transmittance along with the metal-to-insulator transition (MIT) at a critical temperature ∼68 °C. However, low luminous transmittance ( T lum ), poor solar energy modulation ability (Δ T sol ), and high phase transition temperature ( T c ) can limit the application of VO 2 for smart windows. To overcome these limitations, 3D mesoporous structure can be employed in VO 2 films. Herein, 3D mesoporous structures assembled from monoclinic M-phase VO 2 nanoflakes with a pore size of about 2-10 nm were synthesized by a hydrothermal method using Ensete ventricosum fiber (EF) as a template followed by calcination at 450 °C. The prepared film exhibited excellent thermochromic performance with balanced T lum = 67.3%, Δ T sol = 12.5%, and lowering T c to 63.15 °C. This is because the 3D mesoporous structure can offer the uniform dispersion of VO 2 nanoflakes in the film to enhance T lum , ensure sufficient VO 2 nanoflakes in the film for high Δ T sol and lower T c . Therefore, this work can provide a green approach to synthesize 3D mesoporous structures assembled from monoclinic M-phase VO 2 nanoflakes and promote their application in smart windows.