One-step solvothermal synthesis of CsxWO3: Crystal growth regulation by halogen acids with generating oxygen vacancies and W5+ for improving transparent thermal insulation performance

Synthesis of cesium tungsten bronze (Cs x WO 3 ) nanorods with excellent near-infrared shielding performance by a one-step solvothermal method from cheap tungsten source is still challenging. In this work, small-sized Cs x WO 3 nanorods with excellent transparent thermal insulation performance were synthesized by a one-step solvothermal method. It was found that halogen acids played an important role in regulating the growth and microstructure of Cs x WO 3 nanorods. Moreover, different halogen acid can regulate the content of W 5+ =O and oxygen vacancies (V O ) in Cs x WO 3 nanorods, which is helpful to further improve the near-infrared shielding performance of Cs x WO 3 particles. Compared with HF and HBr, the Cs x WO 3 nanoparticles synthesized under the regulation of HCl contain more V O s and W 5+ =O content, showing more excellent near-infrared shielding performance, and the as-prepared Cs x WO 3 -PVA composite film exhibits low haze and high transparency, with the near-infrared light shielding rate at 1500 nm attaining to 97.7% when the visible light transmittance is 71.8%. The thermal insulation test results show that the Cs x WO 3 -PVA composite film synthesized under the regulation of HCl can effectively reduce the indoor temperature by 6.9 °C under the irradiation of sunlight. After 100 cycles of thermal insulation tests, the near-infrared shielding and thermal insulation performance have not declined, showing excellent photothermal stability. This work is of great significance for promoting the industrial production of high-performance Cs x WO 3 nanoparticles and its application in energy-saving windows.