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

Sodium tungsten bronze NaxWO3 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 N2 atmosphere. The prepared powders were confirmed as tetragonal sodium tungsten bronze Na0.1WO3 by X-ray diffraction. The SEM observation showed that the as-prepared Na0.1WO3 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 NaXWO3 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 NaxWO3 exhibited higher visible light transparency with reaching up to about 58% and a downward trend in near-infrared area, which indicates that the prepared Na0.1WO3 have potential application as near-infrared shielding material.