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 (CsxWO3) 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 CsxWO3 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 CsxWO3 nanorods. Moreover, different halogen acid can regulate the content of W5+=O and oxygen vacancies (VO) in CsxWO3 nanorods, which is helpful to further improve the near-infrared shielding performance of CsxWO3 particles. Compared with HF and HBr, the CsxWO3 nanoparticles synthesized under the regulation of HCl contain more VOs and W5+=O content, showing more excellent near-infrared shielding performance, and the as-prepared CsxWO3-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 CsxWO3-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 CsxWO3 nanoparticles and its application in energy-saving windows.