Carrier Dynamics in TiO<sub>2</sub> and Pt/TiO<sub>2</sub> Powders Observed by Femtosecond Time-Resolved Near-Infrared Spectroscopy at a Spectral Region of 0.9−1.5 μm with the Direct Absorption Method

Iwata, Koichi; Takaya, Tomohisa; Hamaguchi, Hiro‐o; Yamakata, Akira; Ishibashi, Teru; Ōnishi, Hiroshi; Kuroda, Haruo

doi:10.1021/jp047531k

Cited by 97 publications

(98 citation statements)

References 51 publications

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“…One of the major findings from studies using ultrafast spectroscopies, is that the trapping timescale of an injected electron is quite short. Most groups concur that trapping of an injected electron occurs on a sub-picosecond time scale [111,386,399,488,512,[528][529][530][531][532][533][534] and possibly shorter than 100 fs [535] depending on the conditions. These observations indicate not only rapid thermalization of the injected electron within the CB, but also that the electron rapidly finds and localizes in particular Ti 3d electronic states, which then 'falls out' of the TiO 2 CB into a shallow donor state (see below).…”

Section: Electron Trappingmentioning

confidence: 98%

A surface science perspective on TiO2 photocatalysis

Henderson

2011

Surface Science Reports

1,838

1,634

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a b s t r a c tThe field of surface science provides a unique approach to understanding bulk, surface and interfacial phenomena occurring during TiO 2 photocatalysis. This review highlights, from a surface science perspective, recent literature that provides molecular-level insights into photon-initiated events occurring at TiO 2 surfaces. Seven key scientific issues are identified in the organization of this review. These are: (1) photon absorption, (2) charge transport and trapping, (3) electron transfer dynamics, (4) the adsorbed state, (5) mechanisms, (6) poisons and promoters, and (7) phase and form. This review ends with a brief examination of several chemical processes (such as water splitting) in which TiO 2 photocatalysis has made significant contributions in the literature.

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Section: Electron Trappingmentioning

confidence: 98%

A surface science perspective on TiO2 photocatalysis

Henderson

2011

Surface Science Reports

1,838

1,634

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“…S2C), although such transients may be quite fast and perhaps no longer obvious after ∼1 ns. Some early reports with Pt, the metal most often used in photocatalytic applications, claimed that the picosecond decay of the electron-hole in either transient absorption or photoluminescence measurements is faster when there is metal present (22,23). However, the reported differences were small, and many of those experiments were carried out using high laser intensities, where carrier annihilation effects become important.…”

Section: Significancementioning

confidence: 99%

Promotion of atomic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H ₂

Joo

Dillon

Lee

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

110

113

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The production of hydrogen from water with semiconductor photocatalysts can be promoted by adding small amounts of metals to their surfaces. The resulting enhancement in photocatalytic activity is commonly attributed to a fast transfer of the excited electrons generated by photon absorption from the semiconductor to the metal, a step that prevents deexcitation back to the ground electronic state. Here we provide experimental evidence that suggests an alternative pathway that does not involve electron transfer to the metal but requires it to act as a catalyst for the recombination of the hydrogen atoms made via the reduction of protons on the surface of the semiconductor instead.photocatalysis | hydrogen production | gold-titania | time-resolved fluorescence | core-shell nanostructures P hotocatalysis is a promising technology to address problems in chemical synthesis (1), environmental remediation (2, 3), and energy utilization (4). The potential for harvesting solar energy and storing it as a chemical fuel using photocatalysts is particularly appealing. Specifically, H 2 may be produced via water splitting this way (5-7). In fact, many photocatalysts have been reported already capable of producing hydrogen out of water, even if none of those are yet commercially viable. Such photocatalysis rely on capturing photon energy via excitation of electrons from the valence band to the conduction band of appropriate semiconductors such as titania, which is often cited as a prototypical example (8-10), creating an excited electron-hole pair that is then used to promote redox reactions (11,12). However, for the photocatalysts to be useful, the lifetime of the electron-hole pair needs to be long enough to be accessible for chemical conversions. The search for photocatalytic systems that fulfill this and other key requirements continues, and would be greatly facilitated by a clearer understanding of the underlying chemical process.It is well known that the addition of metals such as platinum or gold to semiconductors enhances their activity as photocatalysts, in particular for water splitting to produce H 2 (13-15). This effect is currently explained by a mechanism where the excited electrons produced by absorption of light are transferred from the semiconductor to the metal before they have the opportunity to recombine with their corresponding holes and return to the ground electronic state (Fig. 1A) (16-18). In this scheme, the protons from water are reduced on the surface of the metal, in sites physically separated from those on the semiconductor, where oxygen production takes place. Here we present evidence that challenges this conventional explanation, and offer an alternative mechanism for the promotion of photocatalysis by metals. Specifically, using the Au/TiO 2 metal-semiconductor pair as a model system, we show that electron transfer to the metal may not play a significant role in photocatalysis. Instead, the data support a model where the excited electron promotes the reduction of protons on the surface of the se...

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“…26 Hamaguchi has served on the editorial advisory boards of several journals, including Chemical Physics Letters Hiro-o Hamaguchi has made major contributions to the field of vibrational spectroscopy. One of the things that he is passionate about is scientific education and the fostering of young people.…”

Section: Foreword 1507mentioning

confidence: 99%

Foreword

George¹,

Iwata²,

Tahara³

2008

J Raman Spectroscopy

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Carrier Dynamics in TiO₂ and Pt/TiO₂ Powders Observed by Femtosecond Time-Resolved Near-Infrared Spectroscopy at a Spectral Region of 0.9−1.5 μm with the Direct Absorption Method

Cited by 97 publications

References 51 publications

A surface science perspective on TiO2 photocatalysis

A surface science perspective on TiO2 photocatalysis

Promotion of atomic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H ₂

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Carrier Dynamics in TiO2 and Pt/TiO2 Powders Observed by Femtosecond Time-Resolved Near-Infrared Spectroscopy at a Spectral Region of 0.9−1.5 μm with the Direct Absorption Method

Cited by 97 publications

References 51 publications

A surface science perspective on TiO2 photocatalysis

A surface science perspective on TiO2 photocatalysis

Promotion of atomic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H 2

Foreword

Contact Info

Product

Resources

About

Carrier Dynamics in TiO₂ and Pt/TiO₂ Powders Observed by Femtosecond Time-Resolved Near-Infrared Spectroscopy at a Spectral Region of 0.9−1.5 μm with the Direct Absorption Method

Promotion of atomic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H ₂