Facile and controlled synthesis of aligned WO₃ nanorods and nanosheets as an efficient photocatalyst material

In this work, we have performed a facile and controlled synthesis of WO₃ nanorods and sheets in different crystal phases (triclinic, orthorhombic and monoclinic) of WO₃ using the sol-gel method. The detailed structures of the synthesized materials were examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy measurements. The shapes and crystal phases of the WO₃ nanostructures were found to be highly dependent on the calcination temperature. The variation in crystalline phases and shapes is modified the electronic structure of the samples, which causes a variation in the value of optical band gap. The value of the Raman line intensity ratio I₂₆₄/I₃₂₀ has been successfully used to identify the structural transition from the triclinic to the orthorhombic phase of WO₃. The PL spectra of the synthesized products excited at wavelengths 380, 400, and 420nm exhibit intense emission peaks that cover the complete visible range (blue-green-red). The emission peaks at ~460 and ~486nm were caused by the near band-edge and band to band transition, respectively. The peaks in spectral range 500-600nm might be originated from the presence of oxygen vacancies lying within the energy band gap. The synthesized WO₃ nanostructures showed improved photocatalytic activity for the photodegradation of MB dye. The enhanced photocatalytic activity of WO₃ nanosheets compared to WO₃ nanorods for photodegradation of methylene blue (MB) dye could be due to the shape of the nanostructured WO₃. The sheet type of structure provides more active surface for the interaction of dye molecules compared to the rods, which results in a more efficient degradation of the dye molecules.