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Title: From Ba{sub 3}Ta{sub 5}O{sub 14}N to LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2}: Decreasing the optical band gap of a photocatalyst

Abstract

Yellow LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} was successfully synthesized as phase-pure material crystallizing isostructurally to previously reported Ba{sub 3}Ta{sub 5}O{sub 14}N and mixed-valence Ba{sub 3}Ta{sup V}{sub 4}Ta{sup IV}O{sub 15}. The electronic structure of LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} was studied theoretically with the range-separated hybrid method HSE06. The most stable structure was obtained when lanthanum was placed on 2a and nitrogen on 4h sites confirming Pauling's second rule. By incorporating nitrogen, the measured band gap decreases from ∼3.8 eV for the oxide via 2.74 eV for Ba{sub 3}Ta{sub 5}O{sub 14}N to 2.63 eV for the new oxide nitride, giving rise to an absorption band well in the visible-light region. Calculated fundamental band gaps confirm the experimental trend. The atom-projected density of states has large contributions from N2p orbitals close to the valence band edge. These are responsible for the observed band gap reduction. Photocatalytic hydrogen formation was investigated and compared with that of Ba{sub 3}Ta{sub 5}O{sub 14}N revealing significantly higher activity for LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} under UV-light. - Graphical abstract: X-ray powder diffraction pattern of LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} with the results of the Rietveld refinements. Inset: Unit cell of LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} and polyhedralmore » representation of the crystal structure. - Highlights: • Synthesis of a new oxide nitride LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2}. • Refinement of the crystal structure. • Quantum chemical calculations provided band gap close to the measured value. • New phase shows a higher photocatalytic H{sub 2} evolution rate compared to prior tested Ba{sub 3}Ta{sub 5}O{sub 14}N.« less

Authors:
 [1];  [2]; ;  [3];  [1]
  1. Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin (Germany)
  2. Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Universität Bonn, Beringstr. 4, 53115 Bonn (Germany)
  3. Institut für Chemie, Carl von Ossietzky Universität Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg (Germany)
Publication Date:
OSTI Identifier:
22658168
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 246; Other Information: Copyright (c) 2016 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BARIUM COMPOUNDS; CRYSTAL STRUCTURE; ELECTRONIC STRUCTURE; EXPERIMENTAL DATA; NITRIDES; OXIDATION; PHOTOCATALYSIS; SYNTHESIS; TANTALUM COMPOUNDS; X-RAY DIFFRACTION

Citation Formats

Anke, B., Bredow, T., Pilarski, M., Wark, M., and Lerch, M., E-mail: martin.lerch@tu-berlin.de. From Ba{sub 3}Ta{sub 5}O{sub 14}N to LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2}: Decreasing the optical band gap of a photocatalyst. United States: N. p., 2017. Web. doi:10.1016/J.JSSC.2016.11.001.
Anke, B., Bredow, T., Pilarski, M., Wark, M., & Lerch, M., E-mail: martin.lerch@tu-berlin.de. From Ba{sub 3}Ta{sub 5}O{sub 14}N to LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2}: Decreasing the optical band gap of a photocatalyst. United States. doi:10.1016/J.JSSC.2016.11.001.
Anke, B., Bredow, T., Pilarski, M., Wark, M., and Lerch, M., E-mail: martin.lerch@tu-berlin.de. Wed . "From Ba{sub 3}Ta{sub 5}O{sub 14}N to LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2}: Decreasing the optical band gap of a photocatalyst". United States. doi:10.1016/J.JSSC.2016.11.001.
@article{osti_22658168,
title = {From Ba{sub 3}Ta{sub 5}O{sub 14}N to LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2}: Decreasing the optical band gap of a photocatalyst},
author = {Anke, B. and Bredow, T. and Pilarski, M. and Wark, M. and Lerch, M., E-mail: martin.lerch@tu-berlin.de},
abstractNote = {Yellow LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} was successfully synthesized as phase-pure material crystallizing isostructurally to previously reported Ba{sub 3}Ta{sub 5}O{sub 14}N and mixed-valence Ba{sub 3}Ta{sup V}{sub 4}Ta{sup IV}O{sub 15}. The electronic structure of LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} was studied theoretically with the range-separated hybrid method HSE06. The most stable structure was obtained when lanthanum was placed on 2a and nitrogen on 4h sites confirming Pauling's second rule. By incorporating nitrogen, the measured band gap decreases from ∼3.8 eV for the oxide via 2.74 eV for Ba{sub 3}Ta{sub 5}O{sub 14}N to 2.63 eV for the new oxide nitride, giving rise to an absorption band well in the visible-light region. Calculated fundamental band gaps confirm the experimental trend. The atom-projected density of states has large contributions from N2p orbitals close to the valence band edge. These are responsible for the observed band gap reduction. Photocatalytic hydrogen formation was investigated and compared with that of Ba{sub 3}Ta{sub 5}O{sub 14}N revealing significantly higher activity for LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} under UV-light. - Graphical abstract: X-ray powder diffraction pattern of LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} with the results of the Rietveld refinements. Inset: Unit cell of LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2} and polyhedral representation of the crystal structure. - Highlights: • Synthesis of a new oxide nitride LaBa{sub 2}Ta{sub 5}O{sub 13}N{sub 2}. • Refinement of the crystal structure. • Quantum chemical calculations provided band gap close to the measured value. • New phase shows a higher photocatalytic H{sub 2} evolution rate compared to prior tested Ba{sub 3}Ta{sub 5}O{sub 14}N.},
doi = {10.1016/J.JSSC.2016.11.001},
journal = {Journal of Solid State Chemistry},
number = ,
volume = 246,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2017},
month = {Wed Feb 15 00:00:00 EST 2017}
}
  • Hydrothermal reactions of molybdenum-oxide precursors with polyalcohols in the presence of base yielded two series of mixed-valence oxomolybdenum clusters, the hexadecanuclear species [XH{sub 12}(Mo{sup VI}O{sub 3}){sub 4}Mo{sup V}{sub 12}O{sub 40}]{sup m{minus}}(X=Na{sup +}, m=7; X=2H{sup +}, m=6) and the superclusters [XH{sub n}Mo{sup VI}{sub 6}Mo{sup V}{sub 36}O{sub 109}(OCH{sub 2}){sub 3}CR{sub 7}]{sup m{minus}} (X=Na-(H{sub 2}O){sub 3}{sup +}, m=9, n=13; X=Na(H{sub 2}O){sub 3}{sup +}, m=7, n=15; X=MoO{sub 3}, m=9, n=14; X=MoO{sub 3}, m=10, n=13). In a representative synthesis for the hexadencanuclear class of materials, the hydrothermal reaction of a mixture of Na{sub 2}MoO{sub 4}{center_dot}2H{sub 2}O, MoO{sub 3}, Mo metal, and NH{sub 4}Cl produced (NH{submore » 4}){sub 7}[NaMo{sub 16}(OH){sub 12}O{sub 40}]{center_dot}4h{sub 2}O (1{center_dot}4H{sub 2}O) as red-orange crystals. The compound (Me{sub 3}NH){sub 4}K{sub 2}[H{sub 2}Mo{sub 16}(OH){sub 40}]{center_dot}8H{sub 2}O(2{center_dot}8H{sub 2}O(2{center_dot}8H{sub 2}O) was prepared in a similar fashion. The structure of the anion of 1 consists of an {epsilon}-Keggin core H{sub 12}Mo{sub 12}O{sub 40}, capped on four hexagonal faces by MoO{sub 3} units and encapsulating a Na{sup +} cation. The structure of the oxomolybdenum framework of 2 is essentially identical to that of 1; however, the central cavity is now occupied by 2H{sup +}.« less
  • The subsolidus phase equilibria of the Li{sub 2}O-Ta{sub 2}O{sub 5}-B{sub 2}O{sub 3}, K{sub 2}O-Ta{sub 2}O{sub 5}-B{sub 2}O{sub 3} and Li{sub 2}O-WO{sub 3}-B{sub 2}O{sub 3} systems have been investigated mainly by means of the powder X-ray diffraction method. Two ternary compounds, KTaB{sub 2}O{sub 6} and K{sub 3}Ta{sub 3}B{sub 2}O{sub 12} were confirmed in the system K{sub 2}O-Ta{sub 2}O{sub 5}-B{sub 2}O{sub 3}. Crystal structure of compound KTaB{sub 2}O{sub 6} has been refined from X-ray powder diffraction data using the Rietveld method. The compound crystallizes in the orthorhombic, space group Pmn2{sub 1} (No. 31), with lattice parameters a = 7.3253(4) A, b =more » 3.8402(2) A, c = 9.3040(5) A, z = 2 and D{sub calc} = 4.283 g/cm{sup 3}. The powder second harmonic generation (SHG) coefficients of KTaB{sub 2}O{sub 6} and K{sub 3}Ta{sub 3}B{sub 2}O{sub 12} were five times and two times as large as that of KH{sub 2}PO{sub 4} (KDP), respectively.« less
  • Based on X-ray diffraction and electron microscopy it is shown that oxides of the general formula LaBa/sub 2/Cu/sub 3/O/sub 7-delta/ become tetragonal when delta deviates slightly from 0. This tetragonal structure is similar to that of La/sub 3-x/Ba/sub 3+x/Cu/sub 6/O/sub 14+delta/, with a cubic perovskite subcell and triple periodicity. Electron micrographs of these tetragonal oxides show 90/sup 0/ microdomains. Orthorhombic LaBa/sub 2/Cu/sub 3/O/sub 7-delta/ with high T/sub c/ (approx. 77 K) is found only when delta approx. = 0; this sample is subject to formation of twins. Fluorine substitution seems to favor superconductivity.
  • Composites comprised of two semiconducting materials with suitable band gaps and band positions have been reported to be effective at enhancing photocatalytic activity in the visible light region of the electromagnetic spectrum. Here, we report the synthesis, complete structural and physical characterizations, and photocatalytic performance of a series of semiconducting oxide composites. UV light active tantalum oxide (Ta2O5) and visible light active tantalum oxynitride (TaON) and tantalum nitride (Ta 3N 5) were synthesized, and their composites with Bi 2O 3 were prepared in situ using benzyl alcohol as solvent. The composite prepared using equimolar amounts of Bi 2O 3 andmore » Ta 2O 5 leads to the formation of the ternary oxide, bismuth tantalate (BiTaO 4) upon calcination at 1000 °C. The composites and single phase bismuth tantalate formed were characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) surface area measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis diffuse reflectance spectroscopy, and photoluminescence. The photocatalytic activities of the catalysts were evaluated for generation of hydrogen using aqueous methanol solution under visible light irradiation (λ ≥ 420 nm). The results show that as-prepared composite photocatalysts extend the light absorption range and restrict photogenerated charge-carrier recombination, resulting in enhanced photocatalytic activity compared to individual phases. The mechanism for the enhanced photocatalytic activity for the heterostructured composites is elucidated based on observed activity, band positions calculations, and photoluminescence data.« less
  • The following complex oxynitride perovskites have been prepared: LaMg{sub 1/3}Ta{sub 2/3}O{sub 2}N, LaMg{sub 1/2}Ta{sub 1/2}O{sub 5/2}N{sub 1/2}, and BaSc{sub 0.05}Ta{sub 0.95}O{sub 2.1}N{sub 0.9}. Synchrotron X-ray powder diffraction analyses show that LaMg{sub 1/3}Ta{sub 2/3}O{sub 2}N and LaMg{sub 1/2}Ta{sub 1/2}O{sub 5/2}N{sub 1/2} are isostructural to the oxide La{sub 2}Mg(Mg{sub 1/3}Ta{sub 2/3})O{sub 6} (space group P2{sub 1}/n), whereas BaSc{sub 0.05}Ta{sub 0.95}O{sub 2.1}N{sub 0.9} has a simple cubic symmetry similarly to BaTaO{sub 2}N. The orderings of octahedral cations are markedly diminished in the above oxynitrides, as compared with the related oxides such as La{sub 2}Mg(Mg{sub 1/3}Ta{sub 2/3})O{sub 6} and Ba{sub 2}ScTaO{sub 6}. The opticalmore » band gaps are similar for the homologous compositions, LaMg{sub 1/3}Ta{sub 2/3}O{sub 2}N, LaMg{sub 1/2}Ta{sub 1/2}O{sub 5/2}N{sub 1/2} and LaTaON{sub 2} (1.9 eV), and BaSc{sub 0.05}Ta{sub 0.95}O{sub 2.1}N{sub 0.9} and BaTaO{sub 2}N (1.8 eV), while the absorption edges become broader for the complex derivatives. As revealed from the impedance spectroscopic analysis, the oxynitrides have clearly different dielectric components from those of comparable oxides containing Ta{sup 5+}. Impedance spectroscopy reveals interesting capacitor geometry in BaSc{sub 0.05}Ta{sub 0.95}O{sub 2.1}N{sub 0.9} in which the semiconducting oxynitride grains are separated by insulating secondary phases. Most notably BaSc{sub 0.05}Ta{sub 0.95}O{sub 2.1}N{sub 0.9} has a bulk component with a high relative permittivity ({kappa}=7300) and the grain boundary component with an even higher {kappa}. - Graphical abstract: Phase diagram showing the relations among composition and crystal structure in the quaternary La-Mg-Ta-O-N system.« less