Crystallised mesoporous TiO2(A)-VO2(M/R) nanocomposite films with self-cleaning and excellent thermochromic properties

VO2(M/R) (Monoclinic/Rutile) exhibits reversible insulator-metal transition (IMT) near room temperature, and is a widely used film material for thermochromic smart windows. Recent studies have shown that VO2-based nanocomposite coatings show better optical performance (luminous transmittance, T-lum and solar energy modification ability, Delta T-scl) than pure VO2 thin films. In previous studies, we succeeded in preparing VO2-based organic-inorganic (O-I) composite coatings and optimising their optical performance to a level higher than ever reported previously. Compared to O-I composite coatings, inorganic-inorganic (I-I) composite coatings show advantages in weatherability and multifunctions (for example, self-cleaning TiO2-VO2 composites). In this work, we succeeded in dispersing VO2 nanoparticles (NPs) in TiO2 sol by surface modification, and prepared high quality I-I nanocomposite films with comparable optical performance to that of the best pure VO2 thin film. With the help of thermal analysis, a two-step annealing process was developed, and crystallised TiO2(A)(anatase)-VO2(M/ R) composite films were obtained. By introducing mesopores, the optical performance was improved to T-lum = 62.0% (20 degrees C), 60.5% (90 degrees C) and Delta T-sol = 14.6%, which was better than that of any reported VO2-based pure films. In addition, due to the crystallised TiO2(A), these composite films showed self-cleaning properties (a low contact angle and photocatalytic decomposition of organic contaminants).