Adsorption Characteristics of Methylene Blue on WO₃ Nanorods Prepared by Microwave-Assisted Hydrothermal Methods

Nanostructures of WO₃ powders are selected as a dye adsorbent and investigated to understand the effects of specific surface area of WO₃ nanorods on dye-adsorption performance. The synthesis of WO₃ nanorods is performed using microwave-assisted hydrothermal methods within 5 min, with sodium tungstate dihydrate as a precursor and citric acid as a structure-directing agent. The as-synthesized WO₃ nanorods are characterized by x-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, and Brunauer–Emmett–Teller (BET) measurements for their phases, structure, morphology, surface properties, and specific surface area, respectively. The dye-adsorption performance is studied with a methylene blue (MB) solution using UV-visible spectroscopy, and the results agreed well with the Langmuir model of adsorption. The maximum adsorption capacity of the WO₃ nanorods was derived from Langmuir model's fitting. The specific surface area of WO₃ powders synthesized at 150 °C is 52.05 m² g⁻¹; it tended to decrease with increasing synthesis temperature because of the stacking of nanorods. As a result, the adsorption performance of the WO₃ nanorods is improved as the overall specific surface area increased.