Synthesis of tungsten oxide (W18O49) nanosheets utilizing EDTA salt by microwave irradiation method

Research highlights: → We have synthesized tungsten oxide (WO3-δ) nanoparticles by microwave irradiation method for the first time using EDTA as surface modulator. The variation in stoichiometric oxygen content of the annealed samples clearly indicates the role of EDTA in reaction medium. The variation in oxygen content also modified the transparency of the end product confirming the change in optical conductivity. - Abstract: We report the synthesis of crystalline W18O49 with nanosheet like morphology by low cost microwave irradiation method without employing hydrothermal process for the first time. Initially, WO3.H2O was synthesized using ethylenediaminetetraacetic acid (EDTA) as surface modulator. The product was annealed at 600 oC for 6 h in ambient atmosphere in order to obtain anhydrous tungsten oxide W18O49. Powder X-ray diffraction results confirmed the as prepared WO3.H2O to be orthorhombic and W18O49 to be monoclinic phase, respectively. Transmission electron micrographs (TEM) revealed that the W18O49 nanosheets have the average dimensions of the order of 250 nm in length and around 150 nm in width. UV-visible diffusion reflectance spectroscopic (DRS) studies revealed the band gap energies to be 3.28 and 3.47 eV for WO3.H2O and W18O49 samples, respectively. The growth mechanism of two dimensional W18O49 nanosheets is discussed.