Synthesis of Sodium Tungsten Bronze via Hydrothermal Method Assisted by Citric Acid

Sodium tungsten bronze Na x WO 3 powders have been prepared by hydrothermal method using sodium tungstate as raw material and citric acid as reducing agent, followed by annealing under the inert gas N 2 atmosphere. The prepared powders were confirmed as tetragonal sodium tungsten bronze Na 0.1 WO 3 by X-ray diffraction. The SEM observation showed that the as-prepared Na 0.1 WO 3 particles exhibited rod-like morphology with about 20 μm in length and 5 μm in diameter. The influence of pH value of the precursor solution and annealing temperature on the synthesized powders were also investigated. The results indicated that sodium tungsten bronze Na X WO 3 would not be obtained when the pH value of the precursor solution decreased to pH=1 or the annealing temperature was lower than 700°C by this hydrothermal method. Additionally, as the wavelength increasing, the transmittance of prepared Na x WO 3 exhibited higher visible light transparency with reaching up to about 58% and a downward trend in near-infrared area, which indicates that the prepared Na 0.1 WO 3 have potential application as near-infrared shielding material.