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, Tlum and solar energy modification ability, ΔTsol) 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 Tlum = 62.0% (20 °C), 60.5% (90 °C) and ΔTsol = 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).