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Title: Effects of Vanadium Substitution on the Structure and Photocatalytic Behavior of ETS-10

Abstract

A combination of experimental and computational methods has been used to investigate the effects of vanadium doping in ETS-10. Near edge X-ray absorption fine structure (NEXAFS) spectra reveal octahedrally coordinated V{sup IV} and V{sup V} species within V-doped ETS-10 materials, confirming substitution for Ti{sup IV} sites only. Computational models, using hybrid density functional theory/molecular mechanics (DFT/MM) methods, have been developed that contain varying concentrations of V{sup IV} and V{sup V} within the O-M-O (M = Ti, V) chain. Geometry optimizations indicate that V{sup V} substitution leads to larger changes in the local chain geometry than V{sup IV} substitution. Substitution energetics for V{sup IV} and V{sup V} in different sites have been calculated to determine preferred locations of the two species, suggesting that long chains of V{sup V} are not stable and demonstrating the need for both V{sup V} and V{sup IV} within V-substituted materials. Wavefunctions for systems with an electron added or removed are used to identify electron and hole trapping sites associated with the V{sup V} and V{sup IV} doping centers respectively. An increase in photocatalytic activity is predicted at low [V] due to improved charge separation. However photocatalytic activity is expected to decrease at high [V] due tomore » increased carrier recombination. These results are consistent with recent experimental data.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930324
Report Number(s):
BNL-81034-2008-JA
Journal ID: ISSN 1932-7447; TRN: US200904%%519
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry C; Journal Volume: 111; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; PHOTOCATALYSIS; CATALYSTS; VANADIUM; MATERIAL SUBSTITUTION; DOPED MATERIALS; MORPHOLOGY; CALCULATION METHODS; CATALYTIC EFFECTS; national synchrotron light source

Citation Formats

Shough,A., Doren, D., Nash, M., and Lobo, R. Effects of Vanadium Substitution on the Structure and Photocatalytic Behavior of ETS-10. United States: N. p., 2007. Web. doi:10.1021/jp0662247.
Shough,A., Doren, D., Nash, M., & Lobo, R. Effects of Vanadium Substitution on the Structure and Photocatalytic Behavior of ETS-10. United States. doi:10.1021/jp0662247.
Shough,A., Doren, D., Nash, M., and Lobo, R. Mon . "Effects of Vanadium Substitution on the Structure and Photocatalytic Behavior of ETS-10". United States. doi:10.1021/jp0662247.
@article{osti_930324,
title = {Effects of Vanadium Substitution on the Structure and Photocatalytic Behavior of ETS-10},
author = {Shough,A. and Doren, D. and Nash, M. and Lobo, R.},
abstractNote = {A combination of experimental and computational methods has been used to investigate the effects of vanadium doping in ETS-10. Near edge X-ray absorption fine structure (NEXAFS) spectra reveal octahedrally coordinated V{sup IV} and V{sup V} species within V-doped ETS-10 materials, confirming substitution for Ti{sup IV} sites only. Computational models, using hybrid density functional theory/molecular mechanics (DFT/MM) methods, have been developed that contain varying concentrations of V{sup IV} and V{sup V} within the O-M-O (M = Ti, V) chain. Geometry optimizations indicate that V{sup V} substitution leads to larger changes in the local chain geometry than V{sup IV} substitution. Substitution energetics for V{sup IV} and V{sup V} in different sites have been calculated to determine preferred locations of the two species, suggesting that long chains of V{sup V} are not stable and demonstrating the need for both V{sup V} and V{sup IV} within V-substituted materials. Wavefunctions for systems with an electron added or removed are used to identify electron and hole trapping sites associated with the V{sup V} and V{sup IV} doping centers respectively. An increase in photocatalytic activity is predicted at low [V] due to improved charge separation. However photocatalytic activity is expected to decrease at high [V] due to increased carrier recombination. These results are consistent with recent experimental data.},
doi = {10.1021/jp0662247},
journal = {Journal of Physical Chemistry C},
number = 4,
volume = 111,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Various amounts of vanadium have been isomorphously substituted for titanium in ETS-10, creating samples with V/(V+Ti) ratios of 0.13, 0.33, 0.43, and 1.00 and characterized experimentally using Raman, near-edge X-ray absorption fine structure (NEXAFS), X-ray powder diffraction, N{sub 2} adsorption, scanning electron microscopy (SEM), UV/vis spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Raman spectra reveal a disordered chain structure that contains different V-O bonds along with the presence of a V-O-Ti peak. The UV/vis spectra of the vanadium samples have three new absorption features in the visible region at 450, 594, and 850 nm, suggesting both V{sup 4+}more » and V{sup 5+} are present in the samples. NEXAFS results confirm the presence of both V{sup 5+} and V{sup 4+} in the vanadium samples, with a fraction of V{sup 4+} within the range of 0.2-0.4. The addition of vanadium lowers the band gap energy of ETS-10 from 4.32 eV to a minimum of 3.58 eV for the 0.43ETVS-10 sample. Studies of the photocatalytic polymerization of ethylene show that the 594 nm transition has no photocatalytic activity. The visible transition around 450 nm in the vanadium-incorporated samples is photocatalytically active, and the lower-concentration vanadium samples have higher photocatalytic activity than that of ETS-10 and AM-6, the all-vanadium analogue of ETS-10.« less
  • The effect of substitution of up to two Te atoms by Se atoms on the crystal structure, the magnetic and electronic properties has been studied in the system Cr{sub (5+x)}Te{sub 8-y}Se{sub y}. Trigonal basic cells with space group P-3m1 for Cr{sub (1+x)}Q{sub 2} and trigonal supercells (doubling of the unit cell in all directions) with space group P-3m1 for Cr{sub (5+x)}Q{sub 8} ((1+x)=1.27, 1.32, 1.36; (5+x)=5.08, 5.28, 5.44; Q=Te, Se; Te:Se=6:2) have been identified in X-ray powder diffraction patterns and Rietveld refinements as high-temperature and low-temperature phases, respectively. The crystal structures are related to the hexagonal NiAs-type structure with metalmore » vacancies in every second metal layer. The magnetic properties are closely related to the Cr content and the structure type. Cluster-glass and spin-glass behavior at low temperatures are observed for high and low Cr contents, respectively. For the same Cr content, the phases with trigonal basic cells have higher values for the Curie temperature T{sub c} and the freezing temperature T{sub f}, and larger magnetization than those for the phases with trigonal supercells. For the same structure type, the values for T{sub c}/T{sub f} do not show a linear relationship with the change of Cr content but exhibit a V-shape fashion. Our experimental investigations were accompanied by spin-polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) electronic structure calculations. Cr deficiencies as well as atomic disorder on the chalcogen sites was accounted for using the coherent potential approximation (CPA) alloy theory. Calculation of the exchange coupling parameters J{sub ij} provided the basis for subsequent Monte Carlo simulations of the magnetic properties at finite temperatures.« less
  • Graphical abstract: Visible-light-driven Al/BiVO{sub 4} photocatalyst was prepared by a hydrothermal process. After introducing Al, the BiVO{sub 4} particles retain monoclinic scheelite structures and the ability of visible light absorption is enhanced. XPS and FTIR results reveal that the Al ions influence the local structure of the BiVO{sub 4}. The photocatalytic experiments demonstrate that the Al species incorporation can effectively enhance the photocatalytic activity of BiVO{sub 4} due to the existence of distorted VO{sub 4}{sup 3-} tetrahedron and the stronger optical absorption intensity. Highlights: Black-Right-Pointing-Pointer The visible-light-driven Al/BiVO{sub 4} photocatalysts are first prepared in our study. Black-Right-Pointing-Pointer It is foundmore » that Al is introduced into the BiVO{sub 4} lattice successfully. Black-Right-Pointing-Pointer The Al-doped BiVO{sub 4} shows a far higher photocatalytic activity than undoped BiVO{sub 4}. Black-Right-Pointing-Pointer One of the reason for the higher activity is the distorted VO{sub 4}{sup 3-} tetrahedron. Black-Right-Pointing-Pointer Another reason for the higher activity is the strong optical absorption intensity. -- Abstract: Novel visible-light-driven Al/BiVO{sub 4} photocatalysts were synthesized via a facile hydrothermal method for the first time. The samples were characterized by X-ray diffraction, N{sub 2}-sorption, UV-vis diffuse reflectance spectra, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transformed infrared spectra and X-ray photoelectron spectroscopy. The photocatalytic activity of the samples was evaluated by the decomposition of methylene blue under visible light irradiation (400 nm < {lambda} <580 nm) and was compared with that of single-phase BiVO{sub 4}. The results revealed that the introduction of Al can improve photocatalytic performance greatly and different concentration of Al resulted in different photocatalytic activity. The highest activity is obtained by the sample with a doping concentration of 12 at%. The reason for the enhanced photocatalytic activities of Al/BiVO{sub 4} samples was also discussed in this paper.« less
  • At room temperature the linear complex Br/sub 2/Os/sub 3/(CO)/sub 12/ reacts with PPh/sub 3/ and PPh/sub 2/Me to give the substituted product Br/sub 2/Os/sub 3/(CO)/sub 10/(PR/sub 3/)/sub 2/ (approx. 15%), as well as the mononuclear products Os(CO)/sub 4/PR/sub 3/ (approx. 60%) and Br/sub 2/Os(CO)/sub 2/(PR/sub 3/)/sub 2/ (approx. 15%). The mononuclear products are not formed from Br/sub 2/Os/sub 3/(CO)/sub 10/(PR/sub 3/)/sub 2/ under the conditions of the reaction. The reaction is completely stopped by added CCl/sub 4/ or galvinoxyl, suggesting that the formation of both the trinuclear and mononuclear products are radical processes. From the reaction of Br/sub 2/Os/sub 3/(CO)/submore » 12/ with P(OMe)/sub 3/, the trinuclear complex Br/sub 2/Os/sub 3/(CO)/sub 10/(P(OMe)/sub 3/)/sub 2/ is isolated in 53% yield. This complex crystallizes in the centrosymmetric triclinic space group P1 with a = 8.923 (3) A, b = 11.657 (3) A, c = 8.185 (3) A, ..cap alpha.. = 99.48 (3)/sup 0/, ..beta.. = 111.91 (3)/sup 0/, ..gamma.. = 96.28 (3)/sup 0/, and Z = 1.« less