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

In this work, we have performed a facile and controlled synthesis of WO nanorods and sheets in different crystal phases (triclinic, orthorhombic and monoclinic) of WO 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 WO 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 I/I has been successfully used to identify the structural transition from the triclinic to the orthorhombic phase of WO. 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 WO nanostructures showed improved photocatalytic activity for the photodegradation of MB dye. The enhanced photocatalytic activity of WO nanosheets compared to WO nanorods for photodegradation of methylene blue (MB) dye could be due to the shape of the nanostructured WO. 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.