Now showing 1 - 2 of 2
  • Publication
    Comparison of ZrO2, TiO2, and α-Fe2O3 nanotube arrays on Cr(VI) photoreduction fabricated by anodization of Zr, Ti, and Fe foils
    ( 2020-05-01) ;
    Tan W.K.
    ;
    Kawamura G.
    ;
    Matsuda A.
    ;
    Lockman Z.
    This paper presents the fabrication of self-organized ZrO2, TiO2, and α-Fe2O3 nanotube arrays by anodization of Zr, Ti, and Fe foils, respectively in fluoride-containing EG electrolyte at 40 V for 20 min. The as-anodized nanotubes were annealed in a tube furnace at 400 °C for 3 h to induce the crystallization of the oxide film. Morphology, crystal structure, surface properties, and optical properties of the anodic ZrO2 nanotubes (ZNTs), TiO2 nanotubes (TNTs), and α-Fe2O3 nanotubes (FNTs) were characterized by Field-Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Fourier-Transform Infrared (FTIR) spectroscopy, Photoluminescence (PL) spectroscopy, and UV-visible Near-Infrared Diffuse Reflectance Spectra (UV-vis NIR DRS) spectroscopy, respectively. Based on the FESEM and TEM micrographs, ZNTs possessed the longest nanotubes (i.e. 9.6 μm) compared with TNTs and FNTs under the same anodization condition. The aspect ratio of the nanotubes can be arranged in the order of ZNTs > FNTs > TNTs. The surface of the annealed ZNTs, FNTs, and TNTs was enriched with-OH groups to facilitate the Cr(VI) adsorption. According to the UV-vis NIR DRS spectra, strong visible light absorption was observed on the FNTs due to their low band gap. Whereas, the TNTs predominantly absorbs the UV light at λ max = 360 nm. Rapid Cr(VI) removal was observed on FNTs, i.e. 100% after 2 h activated by sunlight with negligible Cr(VI) removal for ZNTs and TNTs. When exposed to UVC (λ = 254 nm), only 39% versus 37% Cr(VI) removal efficiencies were obtained on TNTs and ZNTs after 3 h suggesting sluggish electron transfer due to rapid charge carriers recombination as evident in the PL spectra.
      1
  • Publication
    Synthesis of visible-light active monoclinic wo3 by thermal oxidation of tungsten powder for photoreduction of cr(vi)
    ( 2020-01-01) ;
    Lee, Qiao Ling
    In this paper, visible-light-active monoclinic-WO3 powders were synthesized by thermal oxidation of W powders at 200-1000 °C in air atmosphere. Morphology and crystal structure of annealed W powders were characterized by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), respectively. Based on the SEM and XRD results, a spherical orthorhombic-W3O8 obtained at 200 °C was transformed into a dendritic monoclinic WO2 + tetragonal WO3 + monoclinic WO3 structures at 400 °C accompanied by a color transition from grey into green powders. At 600 °C, yellow monoclinic WO3 + monoclinic WO2.96 powder was produced that ascribed to oxygen vacancies. Photocatalytic activity of the annealed W powders at 1000 °C demonstrated 70.7% Cr(VI) removal after 150 min attributed to the high photoactivity of monoclinic WO3. Nevertheless, the dendritic monoclinic WO2 + tetragonal WO3 + monoclinic WO3 obtained at 400 °C exhibited the lowest Cr(VI) photoreduction i.e. 45.2% suggesting poor photocatalytic activity of monoclinic WO2 and sluggish electron transport at WO2|WO3 interfaces.
      1