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Title: Chemistry in a Confined Space: Characterization of Nitrogen-doped Titanium Oxide Nanotubes Produced by Calcining Ammonium Trititanate Nanotubes
Authors: Chang, Jui-Chun;Tsai, Wei-Je;Chiu, Tsai-Chin;Liu, Chih-Wei;Chao, Jiunn-Hsing;Lin, Chiu-Hsun
Contributors: 化學系
Date: 2011-03
Issue Date: 2013-06-05T09:36:41Z
Publisher: The Royal Society of Chemistry
Abstract: Ammonium trititanate nanotubes ((NH 4) 2Ti 3O 7, abbreviated as NH 4TNT) were produced from sodium trititanate nanotubes (Na 2Ti 3O 7, abbreviated as NaTNT) by ion exchange using 1.0 M NH 4NO 3. Substituting NH 4 + for Na + reduced the band gap energy (E g) of the trititanate nanotubes. Calcining NH 4TNT at 473 K reduced the inter-layer spacing in the nanotube wall, and further reduced the value of E g, yielding NH 4TNT that responded to visible light. As NH 4 + cations were intercalated in the small inter-layer space of NH 4TNT, calcination at 573 K decomposed NH 4 + (NH 4TNT → NH 3 + HTNT) and produced inside the nanotube wall NH 3 gas at a high pressure, which fractured and thereby shortened the nanotubes. Calcination at 573 K also caused a phase transformation from hydrogen trititanate to TiO 2. Calcination at 673 K induced the dehydrogenation of NH 3 molecules that were confined to the nanotube wall, producing interstitial NH 2 species. Calcinations at between 573 and 673 K resulted in the formation of N-TiO 2 (B) nanotubes and N-anatase nanotubes, which have a narrow band gap (2.96 ∼ 2.76 eV) and respond to visible light. Further calcination at ≥ 773 K caused the loss of N species and the disappearance of the tubular pore of the nanotubes. The activities of N-doped TiO 2 nanomaterials that were calcined at various temperatures in degrading methylene blue followed the order: 673 > 573 > 473 >773 > 873 K. The active N species in these N-doped TiO 2 are molecular nitrogen species, including NH 4 + and NH 3 at high concentrations (3.8 ∼ 1.2 atomic %) at 473 and 573 K, and NH 2 at a low concentration (0.4 ∼ 0.2 atomic %) at 673 and 773 K. The nature and concentration of the N species, surface area, the crystallinity and the crystalline composition of the material govern the photocatalytic activity of N-doped TiO 2 that is prepared by calcining the NH 4TNT.
Relation: Journal of Materials Chemistry, 21(12): 4605-4614
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