Preparation of VxW1−xO2(M)@SiO2 ultrathin nanostructures with high optical performance and optimization for smart windows by etching

Abstract

A fast, low-temperature hydrothermal method was introduced to prepare a V_xW_1−xO₂(B) ultrathin nanostructure which can be easily transformed into V_xW_1−xO₂(M) via a fast annealing process in an inert atmosphere. Thermochromic foils coated with ultrathin V_0.98W_0.02O₂(M) nanopowders exhibited unsatisfactory optical properties with a weak solar regulation efficiency (ΔT_sol, 4.6%) and a low luminous transmittance (T_lum-L, 15.73%) in a low-temperature state. Coating the V_xW_1−xO₂(M) nanostructure with a thin shell of SiO₂ can improve the optical performance of the thermochromic foils resulting in ΔT_sol of 7.15% and T_lum-L of 25.74%. Furthermore, etching the V_0.98W_0.02O₂(M)@SiO₂ core–shell nanostructure with diluted hydrochloric acid (HCl) can optimize the optical properties of the thermochromic foils well, resulting in ΔT_sol and T_lum-L of up to 10.18% and 37.37% owing to the decreased size. In summary, we employed a simple method to synthesize V_1−xW_xO₂@SiO₂ ultrathin nanostructures and provided new insight into optimizing VO₂-based thermochromic windows.