Hydrothermal synthesis of WO3 nanorods: pH adjustment stage, additive comparison and photocatalysis activities

Additives as surfactant can affect the structural, morphological, and optical properties of WO3 nanostructures. However, it is important to find optimum amount of additive for obtaining the best nanostructure of WO3. Therefore, the effect of oxalic acid (C2H2O4) and potassium sulfate (K2SO4) concentration as organic and inorganic additives were studied in this work. Also, the effect of pH adjustment stage (before/after oxalic acid addition) in the synthesis process was investigated for the first time. The WO3 nanostructures were characterized by X-ray powder diffraction (XRD), Raman scattering, field emission scanning electron microscopy (FESEM) and diffuse reflection spectroscopy (DRS). In addition, the photocatalysis activities of the samples with suitable properties were studied. The results proved that the WO3 properties can be affected by additive concentration and pH value of the solution. The creation of uniform nanorods (the length to diameter ratio of 9.4) was showed by FESEM analysis due to the addition of K2SO4. The smallest crystallite size (about 24.10 nm) was obtained for the sample synthesized at low concentration of potassium sulfate with the band gap of 2.64 eV (the ratio of Na2WO42H2O:K2SO4 1:3). Furthermore, the 10 mg of synthesized nanorod displayed the meritorious degradation of methylene blue (10 ppm) under UV light and visible light with the degradation efficiency of 88% and 77% in 90 min, respectively.