Bifunctional Template-Induced VO2@SiO2 Dual-Shelled Hollow Nanosphere-Based Coatings for Smart Windows

Thermochromic vanadium dioxide (VO2) as one of the most promising candidates for smart windows has attracted widespread attention in recent years. Excellent optical performances (luminous transmittance, Tlum, and solar modulation efficiency, Δ Tsol) of VO2-based coatings are usually pursued as crucial issues. In the current work, we report an ingenious approach for the synthesis of VO2@SiO2 dual-shell hollow nanospheres (DSHNs) and the preparation of DSHNs thermochromic coatings. A sequential bifunctional template-induced mechanism for the formation of DSHNs was proposed. Because of the unique hollow-core and dual-shell structure, the as-prepared VO2@SiO2 DSHNs coatings exhibited appealing optical performances with enhanced luminous transmittance of 61.8% and solar modulation efficiency of 12.6%, compared with continuous and dense VO2 coatings. It has been proved that the improvement of visible transmittance could be ascribed to the effective reduction of refractive index (from 2.6 to 1.6 at 630 nm). In addition, its excellent thermochromic performance has been confirmed by the model cubes measurements, expressing a great potential as energy-efficient smart windows in high-rise buildings. The bifunctional template-induced synthetic strategy may inspire more facile, efficient and inexpensive processes for development of well-defined multishelled hollow nanostructures for varied applications.