Increasing synthesis yield of K-doped tungsten oxide nanowire using stirred hydrothermal reactor and its near-infrared reflectance property

One-dimensional nanostructured oxides are typically synthesised by the hydrothermal method in a small pressurised reactor under static conditions that usually results in a low synthesis yield. In this reported work, K-doped tungsten oxide (K₂W₄O₁₃) nanowires were synthesised under stirred hydrothermal treatment of hydrous K₂W₄O₁₃ precursor in the presence of K₂SO₄ employed as the shape-directing agent to promote the formation of nanowires. Under static conditions (0 rpm), only 24.6% yield was obtained. The yield was significantly increased with the increase of stirring speed. The yield of 90.3%, almost four times the static condition, was obtained when synthesised under continuous stirring at 500 rpm. The samples synthesised from both the conditions have the same crystal structure, which is K₂W₄O₁₃. However, the difference in particle morphology was observed; the average diameter of 11.4 ± 0.3 nm and the length up to several hundred micrometres were obtained from the stirred condition, while more irregularities of the nanowires (average diameter of 7.1 ± 1.1 nm and very diverse length) were obtained under static conditions. The more uniformity observed under stirred hydrothermal conditions is attributed to the more uniform crystallisation process attained under the stirring condition. A high near-infrared (NIR) reflectance of 91.3% suggests its NIR shielding ability.