UPS and UV spectroscopies combined to position the energy levels of TiO<sub>2</sub> anatase and rutile nanopowders

Maheu, Clément; Cárdenas, Luis; Puzenat, E.; Afanasiev, P.; Geantet, Christophe

doi:10.1039/c8cp04614j

Cited by 130 publications

(109 citation statements)

References 75 publications

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“…Ultraviolet photoelectron spectroscopy (UPS) analysis is widely used for electronic structure characterisation, ultraviolet light increase the detection sensitivity concomitant with the high photoionization cross-sections in the valence band region [58]. We have developed a methodology to study nanopowders by UPS [59,60].…”

Section: Ups and Diffuse Reflectance Spectroscopymentioning

confidence: 99%

Photocatalytic production of H2 is a multi-criteria optimization problem: Case study of RuS2/TiO2

et al. 2021

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Many parameters influence the photocatalytic production of H 2. Identifying and quantifying them is necessary for correct comparison of photocatalysts and right understanding of involved mechanism. In this work, we studied the photocatalytic dehydrogenation of isopropanol with titania-supported ruthenium disulfide. We studied the influence of seven parameters on the photocatalytic activity: the temperature, the composition of the reactive mixture, the mass of the photocatalyst, the flux and the energy of the incident photons, the co-catalyst loading and the nature of the support. Their influence was studied, not only on the rate of hydrogen production (or photon yield) but also on the apparent activation energy and on the preexponential factor, deduced from an Arrhenius law. The photon yield as a function of the co-catalyst loading show an optimum of activity. A 6.9 % photon yield was obtained at 0.84 wt% and = 3.65. The rate-determining step for the photocatalytic dehydrogenation of the isopropanol with RuS 2 /TiO 2 is, at optimal conditions, the electron transfer from TiO 2 to RuS 2. The latter is not favored because of the band diagrams of RuS 2 and TiO 2. The electron transfer can be optimized working with incident photons having a higher energy, thanks to a hot carrier effect observed in RuS 2 /TiO 2 .

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Section: Ups and Diffuse Reflectance Spectroscopymentioning

confidence: 99%

Photocatalytic production of H2 is a multi-criteria optimization problem: Case study of RuS2/TiO2

et al. 2021

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“…The methodology developed in Maheu et al was applied to the oxysulfides powders. 43 and I signal is plotted (I signal = I exp -I background ). 54 Spectra were normalized to compare significant variations of the density of states.…”

Section: Ultraviolet Photoelectron Spectroscopymentioning

confidence: 99%

Band Gap Engineering from Cation Balance: The Case of Lanthanide Oxysulfide Nanoparticles

et al. 2019

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Among the inorganic compounds, many oxides and sulfides are known to be semiconductors. At the crossroads of these two families, oxysulfide M x O y S z compounds were much less investigated because they are scarce in nature and complex to synthesize. Among them, lanthanide oxysulfide Ln 2 O 2 S (Ln = lanthanide) are indirect band gap semiconductors, with wide gaps, except for Ce 2 O 2 S. (Gd,Ce) 2 O 2 S anisotropic nanoparticles with a hexagonal structure were obtained over the whole composition range and exhibit colors varying from white to brown with increasing Ce concentration. Band gap engineering is thus possible, from 4.7 eV for Gd 2 O 2 S to 2.1 eV for Gd 0.6 Ce 1.4 O 2 S, while the structure is preserved with a slight lattice expansion. Surprisingly, because of the limited thickness of the lamellar nanoparticles, the band gap of the nanoparticles is direct as validated by density functional theory on slabs. The fine control of the band gap over a wide range, solely triggered by the cation ratio, is rarely described in the literature and is highly promising for further development of this class of compounds. We propose a multiregime mechanism to rationalize the band gap engineering over the whole composition range. This should inspire the design of other bimetallic nanoscaled compounds, in particular, in the field of visible light photocatalysis.

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“…According to ref. [55], for anatase the offsets of conduction and valence band are, respectively E CB = À 3.95 eV, E VB = À 7.1 eV, the band gap E g = 3.15 eV, hence for intrinsic anatase TiO 2 the work function may be computed as Φ = 5.53 eV. For heavily n-doped material Φ would decrease by E g /4, [56] i. e. it yields 4.74 eV, while for heavily p-doped the work function would increase by E g /4, yielding 6.31 eV.…”

Section: Surface Characterizationmentioning

confidence: 99%

Degenerated TiO₂ Semiconductor Modified with Ni and Zn as Efficient Photocatalysts for the Water Splitting Reaction

et al. 2020

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The development of robust, safe, cost-effective and efficient photocatalytic systems for water splitting should take into account the presence of a proper and powerful photon absorber and an efficient, low-cost and earth-abundant electrocatalyst to perform the reaction at high conversions. In this study, NiÀ Zn/TiO 2 ternary composites with high photocatalytic activity for water splitting under UV irradiation were successfully prepared via a simple and low-cost deposition-precipitation route. Thus, different Ni : Zn molar ratios (1 : 0, 1 : 1, 3 : 1, 6 : 1, 9 : 1, and 0 : 1) were deposited on TiO 2 in order to reach a total metal loading of 50 wt. %. The obtained composites were characterized using several techniques, such as: X-ray diffrac-tion, UV-Vis spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The most active synthesized composite, namely NiÀ Zn/ TiO 2 (9 : 1), exhibits H 2 generation rate above 17 mmols g À 1 h À 1 , which is nearly one thousand times higher than that obtained with TiO 2 Evonik P25. Our study demonstrates that TiO 2 becomes a degenerated semiconductor in the presence of Ni and ZnO, with remarkable photocatalytic properties. Thus, the obtained results can open new opportunities in the preparation of very active materials for hydrogen production based on the optimization of three-component structures.

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UPS and UV spectroscopies combined to position the energy levels of TiO₂ anatase and rutile nanopowders

Abstract: Positioning of absolute energy levels and the quantitative description of occupied levels obtained for TiO2 nanopowders, combining UPS and UV-Vis spectroscopies.

Cited by 130 publications

References 75 publications

Photocatalytic production of H2 is a multi-criteria optimization problem: Case study of RuS2/TiO2

Photocatalytic production of H2 is a multi-criteria optimization problem: Case study of RuS2/TiO2

Band Gap Engineering from Cation Balance: The Case of Lanthanide Oxysulfide Nanoparticles

Degenerated TiO₂ Semiconductor Modified with Ni and Zn as Efficient Photocatalysts for the Water Splitting Reaction

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UPS and UV spectroscopies combined to position the energy levels of TiO2 anatase and rutile nanopowders

Abstract: Positioning of absolute energy levels and the quantitative description of occupied levels obtained for TiO2 nanopowders, combining UPS and UV-Vis spectroscopies.

Cited by 130 publications

References 75 publications

Photocatalytic production of H2 is a multi-criteria optimization problem: Case study of RuS2/TiO2

Photocatalytic production of H2 is a multi-criteria optimization problem: Case study of RuS2/TiO2

Band Gap Engineering from Cation Balance: The Case of Lanthanide Oxysulfide Nanoparticles

Degenerated TiO2 Semiconductor Modified with Ni and Zn as Efficient Photocatalysts for the Water Splitting Reaction

Contact Info

Product

Resources

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UPS and UV spectroscopies combined to position the energy levels of TiO₂ anatase and rutile nanopowders

Degenerated TiO₂ Semiconductor Modified with Ni and Zn as Efficient Photocatalysts for the Water Splitting Reaction