A fingerprint of metal-oxide powders: energy-resolved distribution of electron traps

Nitta, Akio; Takase, Mai; Takashima, Mai; Murakami, Naoya; Ohtani, Bunsho

doi:10.1039/c6cc04999k

Cited by 91 publications

(132 citation statements)

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“…i , can be experimentally confirmed by means of electron spin resonance (ESR) [38][39][40][41][42], infrared radiation (IR) [40,[42][43][44][45][46][47][48], ultraviolet-visible absorption (UV-vis) [14,42,[49][50][51], photoluminescence (PL) [52], photoacoustic [53][54][55][56], and photoelectron spectroscopies [17,18,30]. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are powerful tools for the direct observation of surface Ti ds [17,18,30,[57][58][59].…”

Section: •••mentioning

confidence: 99%

“…Notably, the relative position between the Ti ds energy distributed within the bandgap and the acceptor level of the AP derivatives (the solid Gaussian curve) should be appropriate ( Figure 5) [72]. The energy distribution of Ti ds in TiO 2 powders and colloids can be obtained by photochemical [60], electrochemical [61,62], and RDB-PAS [56] methods. The acceptor levels of AP derivatives can be estimated by the Marcus theory [72,[74][75][76].…”

Section: Hydrogenation Of Carbonyl Compoundsmentioning

confidence: 99%

“…Therefore, the information from the theoretical calculations and the photoelectron spectroscopy, applied to the clean catalyst surfaces under ultra-high vacuum conditions, may be limited for actual photocatalytic systems. To address this issue, Ohtani et al developed a powerful tool for measuring the energy-resolved distribution of electron trap states for many types of TiO 2 powders, composed of anatase, rutile, and brookite in methanol-containing gas phase, by means of reversed double-beam photoacoustic spectroscopy (RDB-PAS) [56]. They showed that the electron energy of the trap states is distributed around the CB edge of TiO 2 and the distribution range of anatase TiO 2 is relatively broader than that of rutile TiO 2 ( Figure 2).…”

Section: ••mentioning

confidence: 99%

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Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis

2017

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Electrons, photogenerated in conduction bands (CB) and trapped in electron trap defects (Ti ds ) in titanium dioxide (TiO 2 ), play crucial roles in characteristic reductive reactions. This review summarizes the recent progress in the research on electron transfer in photo-excited TiO 2 . Particularly, the reactivity of electrons accumulated in CB and trapped at Ti ds on TiO 2 is highlighted in the reduction of molecular oxygen and molecular nitrogen, and the hydrogenation and dehalogenation of organic substrates. Finally, the prospects for developing highly active TiO 2 photocatalysts are discussed.

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Section: •••mentioning

confidence: 99%

Section: Hydrogenation Of Carbonyl Compoundsmentioning

confidence: 99%

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Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis

2017

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“…It has been reported in a recent paper from the present author's group that ERDT as well as the CBB as a function of energy from the VB top can be measured by reversed double-beam photocatalytic spectroscopy (RDB-PAS), in which electrons in the VB are directly excited to ETs, and the accumulation of electrons filling ETs from the deep-energy side to shallow-energy side is recorded [8]. The ERDT/CBB patterns of more than 30 commercially or non-profitably available titania samples showed that all of the titania samples possess shallow ETs near the CBB and detectable/negligible deep ETs, and those ERDT/CBB patterns were different.…”

Section: "Semiconductor" Photocatalysismentioning

confidence: 99%

Hidden but Possibly Fatal Misconceptions in Photocatalysis Studies: A Short Critical Review

Ohtani

2016

Catalysts

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“…Continued use of the BSM is because no methods have been developed to measure the surface structural properties using macroscopic measurements, rather than microscopic measurements such as transmission electron microscopy or atomic force microscopy. To the authors' knowledge, reversed double-beam photoacoustic spectroscopy (RDB-PAS) has been developed to analyze the energy-resolved distribution of electron traps (ERDT), which reflect the surface structure of semiconductor solids (powder), including a wide range of metal oxides as the sole macroscopic analytical method [5,6].A number of papers have been published on the preparation, characterization, and photocatalytic activities of titania photocatalysts modified through doping, loading, and/or mixing heteroatoms [1,2], in which characterization was performed by X-ray diffractometry (XRD), nitrogen-adsorption measurement, and/or scanning electron microscopy. That is, no surface-structural analysis has been conducted, and the photocatalytic activity-photocatalyst property correlation seems to have been discussed without using surface-structural information.In the present paper, copper [7,8] and cerium-modified [9,10] samples were synthesized using the sol-gel method, while the Pt-modified [11] sample was prepared using the impregnation method.…”

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Correlation of the Photocatalytic Activities of Cu, Ce and/or Pt-Modified Titania Particles with their Bulk and Surface Structures Studied by Reversed Double-Beam Photoacoustic Spectroscopy

et al. 2019

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Modified titania photocatalyst powder samples were prepared using the sol-gel method for copper (Cu) and cerium (Ce) doping and impregnation for platinum (Pt) loading. Their bulk crystalline structures were investigated using X-ray diffractometry (XRD) with the Rietveld analysis. The surface/bulk structure, surface properties, and morphologies were observed using reversed double-beam photoacoustic spectroscopy (RDB-PAS), nitrogen adsorption, and scanning electron microscopy, respectively. The results from the XRD revealed that all samples were mainly anatase (ca. 80% or higher) with small amounts of rutile and non-crystalline components. The specific surface areas of all samples were in the range of 115-155 m 2 g −1 . Ce and Cu species were mainly distributed, while Pt was potentially loaded as a partially oxidized form on the titania surface. The results from the RDB-PAS indicated the changing of the energy-resolved distribution of electron traps (ERDT) from the original titania surface upon doping of the metals (Cu, Ce, and Pt), which altered their catalytic activities. The metals photocatalytic activities with UV irradiation were measured in two representative reactions; (a) CO 2 evolution from acetic acid under the aerobic condition and (b) H 2 evolution from deaerated aqueous methanol. In reaction (a), the Cu and/or Ce modification gave almost the same or slightly lower activity compared to the non-modified titania samples, while platinum loading yielded ca. 5-6 times higher activity. For reaction (b), the photocatalytic tests were divided into two sets; without (b 1 ) and with (b 2 ) Pt deposition during the reaction. Similar enhancements of activity from the Pt loading sample (and by Cu modification) were observed in reaction (b 1 ) without in-situ platinum deposition, while the unmodified and Ce-doped samples were almost inactive. For the activities of reaction (b 2 ) with in-situ platinum deposition, the unmodified samples showed the highest activity while the Cu-modified samples showed significantly lower activity. deposition under UV-light irradiation [1][2][3][4]. The basic principle for these photocatalytic reactions is that a photoexcited electron in a conduction band and a positive hole in a valence band, created by UV photoabsorption of titania photocatalysts, will reduce and oxidize, respectively, the surface-adsorbed substrates. The band-structure model (BSM) has been used, not limited to titania photocatalysis, for the explanation of reaction mechanisms, as well as the difference in photocatalytic activities. However, the photocatalytic reaction rates probably depend on the type and surface properties of the photocatalysts. The limitations of using the BSM to describe the relationship between photocatalyst properties and photocatalytic activities are that the BSM does not include information on the surface structure/property of photocatalyst particles and it does not include the description on the surface structure, where electrons and positive holes are transferred to the surface-adsorbed subs...

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A fingerprint of metal-oxide powders: energy-resolved distribution of electron traps

Cited by 91 publications

References 11 publications

Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis

Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis

Hidden but Possibly Fatal Misconceptions in Photocatalysis Studies: A Short Critical Review

Correlation of the Photocatalytic Activities of Cu, Ce and/or Pt-Modified Titania Particles with their Bulk and Surface Structures Studied by Reversed Double-Beam Photoacoustic Spectroscopy

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