Synthesis of One-Dimensional Hexagonal Sodium Tungsten Oxide and Its Near-Infrared Shielding Property

Sodium tungstate nanofibers have been successfully synthesized via a facile hydrothermal reaction route in the presence of sulfate. The as-prepared sodium tungstate nanofibers exhibited great homogenity with diameters of 200-300 nm and length of 15-20 mu m. The results also suggested that atomic ratio of Na/W and aspect ratio of nanofibers can be easily adjusted by changing the concentration of Na2SO4 in the starting materials. After reduction under an atmosphere of H-2 (5 vol.%)/N-2, the sodium tungstate transformed to sodium tungsten bronze without loss of one-dimensional nanostructure. The sodium tungstate (MxWO3+x/2) showed no NIR shielding performance, however, the sodium tungsten bronze (MxWO3) with high content of sodium showed promising optical characteristics such as high transmittance for visible lights as well as high shielding performance for near-infrared lights, indicating its potential application as solar filter. It was observed that NIR shielding performance increased with increment of Na/W atomic ratio while the transparency in visible light region was almost the same.