Now showing 1 - 3 of 3
  • Publication
    Formation of self-organized ZrO2-TiO2and ZrTiO4-TiO2nanotube arrays by anodization of Ti-40Zr foil for Cr(VI) removal
    ( 2022-07-01) ;
    Tan W.K.
    ;
    Kawamura G.
    ;
    Matsuda A.
    ;
    Lockman Z.
    In this work, anodic oxidation of Ti-40 wt.% Zr alloy in EG/NH4F/H2O electrolyte was done to produce anodic self-aligned oxide nanotube arrays. The nanotubes were amorphous but upon annealing at 400° C they were crystallized into ZrO2-TiO2 nanotubes and ZrTiO4-TiO2 nanotubes at 600 °C. The nanotubes were used to reduce 60 ppm Cr(VI) ions under sunlight or UV irradiation. 100% removal of Cr(VI) was achieved on ZrTiO4-TiO2 nanotubes after 5 h of exposure to UV light but only 53% removal was obtained on ZrO2-TiO2 nanotubes. The higher photocatalytic activity of the ZrTiO4-TiO2 nanotubes can be related to the presence of the ZrTiO4 phase which has good acid-base properties as well as the junction formation between ZrTiO4 and TiO2 that can further enhance the reduction process.
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  • Publication
    Formation of Fe-doped ZrOâ‚‚ nanotube arrays in glycerol/formamide at varying fluoride content for Cr(VI) photoreduction
    ( 2024-01-01)
    Hanis Nadirah Che Fauzi N.
    ;
    ;
    Juliana Jelaini F.
    ;
    Lockman Z.
    Fe-doped ZrO2nanotubes (Fe-ZNTs) were produced by anodizing a Zr-5 wt% Fe (Zr-5Fe) alloy in a mixture of fluoride-containing glycerol/formamide (FA) (1:1 ratio)/1 vol% H2O at 50 V for 3 h in different concentrations of ammonium fluoride (NH4F) (0.3, 0.5, and 1.0 wt%). These materials were synthesized to serve as photocatalysts for the removal of hexavalent chromium, Cr(VI) ions by photoreduction. To crystallize the oxide film, the as-anodized Fe-ZNTs were subjected to annealing at 500 °C for 3 h in a tube furnace. The morphology and crystal structure of the annealed Fe-ZNTs were analyzed using Field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), respectively. The surface functional groups and surface chemical of the samples were analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. The formation of hollow structure of the Fe-ZNT was validated by High-resolution transmission electron microscopy (HRTEM). The dimensions of the Fe-ZNTs were measured using Image J. UV-Visible spectroscopy was used to determine the Cr(VI) concentration remaining in the sample after photoreduction. From the FESEM micrographs, the diameter of the Fe-ZNTs was enlarged with higher fluoride content, while the length abruptly decreased due to excessive etching of the oxide film at oxide|electrolyte interface. The XRD results indicate the high intensity of tetragonal-ZrO2in high fluoride content after annealing. From the photocatalytic results of 30 ppm Cr(VI) under sunlight, the Fe-ZNTs synthesized in 1.0 wt% NH4F exhibited the highest Cr(VI) removal efficiency with 100 % after 5 h due to enhanced Cr(VI) adsorption and high photoactivity of tetragonal-ZrO2
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  • 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.
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