Time-resolved infrared absorption spectroscopy of photogenerated electrons in platinized TiO2 particles

Yamakata, Akira; Ishibashi, Teru; Ōnishi, Hiroshi

doi:10.1016/s0009-2614(00)01374-9

Cited by 200 publications

(304 citation statements)

References 19 publications

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“…Thus, rutile may not be expected to exhibit the shallow trap IR absorption observed here for the anatase samples with large particle sizes (Figure 3d). From this it can be concluded that not only are the shallow traps reported here and elsewhere 13,17,23,24 associated with anatase but that they are also associated with larger particles (g30 nm).…”

supporting

confidence: 70%

Apparent Semiconductor Type Reversal in Anatase TiO₂ Nanocrystalline Films

et al. 2007

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The electronic properties of anatase and rutile TiO 2 polycrystalline particle films have been studied using surface photovoltage (SPV) and infrared (IR) spectroscopies. The films were prepared from aqueous suspensions using a range of particle sizes (8-400 nm) and were examined under different ambient conditions. The results show that all of the examined films exhibited the expected n-type semiconductor characteristics in dry nitrogen ambient. Films created from the 30 and 400 nm anatase particles exhibited the largest surface photovoltage and also a broad mid-IR absorption attributed to shallowly trapped electrons. The latter was absent from films made from rutile particles. When examined under as-prepared "wet" conditions, the SPV was reduced in magnitude and the IR signal was absent. Further, the films formed from 8 and 30 nm particles exhibited an apparent p-type behavior in their SPV spectra. Interestingly, small anatase particles are known to exhibit enhanced photocatalytic activity when compared to larger anatase particles. These correlations indicate that water, adsorbed on TiO 2 particles of nanodimensions, induce surface states and enable redistribution of photogenerated charge carriers, which is conducive to photocatalysis.Photocatalysis at semiconductor surfaces has been extensively investigated over recent decades. 1-3 Titanium dioxide has usually been the photocatalyst of choice and Degussa P25, which contains about 80% anatase and 20% rutile, has emerged as the benchmark material. 3 Photocatalysis studies have spanned well-characterized, single-crystal (usually rutile) surfaces under ultrahigh vacuum (UHV) conditions 4-6 to polycrystalline powders under catalysis operational conditions. 7-9 The latter have generally involved the catalyst in contact with an aqueous solution or water vapor. It is acknowledged that the presence of water is important for photocatalysis, 10-11 but its exact role in the process is poorly understood. 12-15 Numerous models 13,[16][17][18][19] have been proposed for the influence of adsorbed water on charge carrier trapping but consensus has still to be reached.Surface photovoltage (SPV) spectroscopy has been used to study both polycrystalline and single crystal (110) rutile TiO 2 . [20][21][22] For both types of material, it was reported that water modified the surface work function of rutile TiO 2 surfaces. There appear to have been no corresponding studies of anatase TiO 2 surfaces. It has been observed that adsorbed water influences a broad mid-infrared spectral absorption between 4000 and 700 cm -1 , which arises when TiO 2 polycrystalline films are irradiated with UV light 13,17,23,24 and that has been assigned to excitation of shallowly trapped electrons. 24 Panyatov and Yates 17 observed that this signal decreases when water is chemisorbed to the surface of a thermally reduced P25 TiO 2 film. They propose that the water depletes conduction band electrons during the formation of Ti-OH groups in the early stages of chemisorption. In this paper, we report the results...

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supporting

confidence: 70%

Apparent Semiconductor Type Reversal in Anatase TiO₂ Nanocrystalline Films

et al. 2007

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“…In these differences in spectra (a spectrum recorded before UV exposure is subtracted from the spectrum recorded after UV exposure), we clearly observe a main feature localized at 910 cm −1 along with two additional features at 1205 and 1375 cm −1 . The observation of such UV-induced features in TiO 2 has been reported previously for titania powders by Yates and co-workers [89][90][91][92][93][94][95]. However, in this earlier powder data, the sharper features at 1205 and 1375 cm −1 could not be identified.…”

Section: Photocatalytic Co Oxidation On Rutile and Anatase [3639]supporting

confidence: 54%

IR spectroscopy applied to metal oxide surfaces: adsorbate vibrations and beyond

Yang

Wöll

2017

Advances in Physics: X

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Metal oxides are among the technologically most important materials. Almost all metals are covered by one oxide layer under ambient conditions. The characterization of oxide surface properties, therefore, is still attracting an increasing amount of attention in surface science. A challenge is provided by the fact that these materials cannot be studied with standard techniques in a straightforward fashion. In this review, we summarize recent results obtained by IRspectroscopy applied in a reflection-geometry to macroscopic oxide monocrystals. These results provide new insights in the adsorption and subsequent reactions and photoreactions of molecules on these highly interesting, very complex class of materials. In addition, the IR-spectroscopy can also be used to probe photophysical properties, e.g. the generation and decay of electron or hole polarons.

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“…However, this doubt was denied after the transient IR absorption spectra of both P25-TiO 2 and novel TiO 2 (A) were determined. The transient IR absorption of 1000-3000 cm 1 is a powerful tool for investigating the lifetime of the photo-generated electrons in the conduction band [35][36][37]. …”

Section: Transient Ir Absorptionmentioning

confidence: 99%

A novel TiO2 with a large amount of bulk intrinsic defects—Visible-light-responded photocatalytic activity induced by foreign trap

Zhang

Jin

et al. 2013

Chin. Sci. Bull.

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A novel TiO 2 (anatase) containing a large amount of single electron trapped oxygen vacancies (SETOV) was prepared by dehydration of titanic acid nanotubes. This novel TiO 2 contains high concentration intrinsic defects in bulk structure, while its surface still remains the stoichiometric structure to protect them. And this novel TiO 2 itself has the visible light absorption without any doping, so we call it as the third generation of TiO 2 . However, it is regretted that this novel TiO 2 (A) only has photocatalytic activity under UV light irradiation, and was inactive for the visible light. The true reasons for this phenomenon were investigated by the transient IR absorption and photoluminescence spectra. Through constructing the foreign electron traps (PdO, PtO 2 ), the photocatalytic oxidation of propylene under visible light irradiation was successfully achieved. The removal yield of propylene (C 3 H 6 ) reached 7.6% and 28% on 2 wt.% PtO 2 /novel TiO 2 and 2 wt.% PdO/novel TiO 2 , respectively. By comparison with the noble metal electron traps (Pt, Pd), we found that the effective foreign electron traps need to satisfy two conditions: (1) Fe, Pb, Cu,. They can extend the photoresponse of TiO 2 to the visible light region, however, the doped metal ions can also play the role of the recombination centers to reduce its photocatalytic activity [7]; (2) nonmetalic ions, such as C, N, F, P, S, etc. Recently, much attention has been focused on the nitrogen doping [8][9][10][11][12][13]. It should be emphasized is that the origin of the visible-lightresponded photocatalytic activity of N-doped TiO 2 still remains disputable [14][15][16][17][18][19]. The redox potential of the doped nitrogen (e.g. -NO) exists within V cb to V vb of TiO 2 [20], so the photoelectrochemical stability of the N-doped TiO 2 may be a question for the practical application. In addition to the non-intrinsic defects can make the photo-response of TiO 2 red-shift, the intrinsic defects can also play the same role. As well known, when TiO 2 was reduced in H 2 atmosphere or treated under vacuum at high temperature, two kinds of intrinsic defects (i.e. oxygen vacancies denoted as V o˙˙, and Ti 3+ ) would form on TiO 2 surface simultaneously [21][22][23]. The energy levels of both in-

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Time-resolved infrared absorption spectroscopy of photogenerated electrons in platinized TiO2 particles

Cited by 200 publications

References 19 publications

Apparent Semiconductor Type Reversal in Anatase TiO₂ Nanocrystalline Films

Apparent Semiconductor Type Reversal in Anatase TiO₂ Nanocrystalline Films

IR spectroscopy applied to metal oxide surfaces: adsorbate vibrations and beyond

A novel TiO2 with a large amount of bulk intrinsic defects—Visible-light-responded photocatalytic activity induced by foreign trap

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Time-resolved infrared absorption spectroscopy of photogenerated electrons in platinized TiO2 particles

Cited by 200 publications

References 19 publications

Apparent Semiconductor Type Reversal in Anatase TiO2 Nanocrystalline Films

Apparent Semiconductor Type Reversal in Anatase TiO2 Nanocrystalline Films

IR spectroscopy applied to metal oxide surfaces: adsorbate vibrations and beyond

A novel TiO2 with a large amount of bulk intrinsic defects—Visible-light-responded photocatalytic activity induced by foreign trap

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Apparent Semiconductor Type Reversal in Anatase TiO₂ Nanocrystalline Films

Apparent Semiconductor Type Reversal in Anatase TiO₂ Nanocrystalline Films