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

Abstract

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.