Hydrothermal synthesis and characterization of WO₃ nanostructures: effects of capping agent and pH

The hydrothermal method as a simple, one-step, cost-effective, environmental compatible technique has been used to synthesize tungsten oxide nanostructures from sodium tungstate as precursor material. The effects of capping agent and pH value of solution on the structural, morphological, chemical bonding, and optical properties of products have been thoroughly investigated by using x-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy-dispersive x-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), and Diffuse reflectance spectroscopy (DRS), respectively. The results indicated that the type of capping agent used in the synthesis procedure strongly affects the growth mechanism and final crystalline structure of the product. Also, the pH value of the solution is a remarkable parameter that controls morphology, crystalline phase, and optical properties of the sample. Phase transition and shape evolution have been observed during pH increment. It was found that decreasing the pH leads to the formation of nanostructures with smaller bandgaps and blue-shift emerges at the optical absorption edges so, synthesized WO₃ nanostructures showed tunable wide bandgap and therefore could have promising optical applications. (paper)