Role of Microwave on Structural, Morphological, Optical and Visible Light Photocatalytic Performance of WO3 Nanostructures

A novel, energy efficient and facile one step microwave irradiation method has been adopted to prepare the WO3 nanostructures without using any post annealing process. The WO3 nanoparticles were synthesized from tungstic acid and sodium hydroxide mixed aqueous solutions exposed for 5min to microwave radiation at four different powers, namely 180, 360, 720 and 900W. The as-synthesized product was characterized using structural, morphological and optical studies by powder X-ray diffraction (PXRD), scanning electron microscope, transmission electron microscope (TEM), Raman spectroscopy, photoluminescence spectroscopy (PL) and UV-visible diffuse reflectance (DRS) analysis. Nanocrystalline monoclinic structures of WO3 with different nanoscale were obtained through XRD and TEM analysis. The average grain size of the WO3 was increased from 20 to 38nm with the increase of microwave power. A considerable red shift and decreasing the band gap energy was observed with the increase of microwave power. The photocatalytic efficiencies of the WO3 catalyst powders were investigated by using two different dyes such as Methylene blue and Congo red under visible light irradiation. The 900W irradiated sample showed excellent catalytic efficiency and stability than other samples. The possible growth and photocatalytic mechanisms for these WO3 nanostructures were tentatively proposed.