Comparison of the morphology and structure of WO₃ nanomaterials synthesized by a sol-gel method followed by calcination or hydrothermal treatment

Tungsten (VI) oxide (WO₃) nanomaterials were synthesized by a sol-gel method using WCl₆ and C₂H₅OH as precursors followed by calcination or hydrothermal treatment. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) equipped with energy dispersive X-ray spectroscopy (EDX) were used to characterize the structure and morphology of the materials. There were significant differences between the WO₃ materials that were calcinated and those that were subjected to a hydrothermal process. The XRD results revealed that calcination temperatures of 300°C and 400°C gave hexagonal structures and temperatures of 500°C and 600°C gave monoclinic structures. The SEM images showed that an increase in calcination temperature led to a decrease in the WO₃ powder particle size. The TEM analysis showed that several nanoparticles agglomerated to form bigger clusters. The hydrothermal process produced hexagonal structures for holding times of 12, 16, and 20 h and monoclinic structures for a holding time of 24 h. The SEM results showed transparent rectangular particles which according to the TEM results originated from the aggregation of several nanotubes.