Double-Beam Photoacoustic Spectroscopic Studies on Transient Absorption of Titanium(IV) Oxide Photocatalyst Powders

Murakami, Naoya; Mahaney, Orlando Omar Prieto; Abe, Ryu; Torimoto, Tsukasa; Ohtani, Bunsho

doi:10.1021/jp071362x

Cited by 87 publications

(81 citation statements)

References 51 publications

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“…Since the electron transfer from gold to 5 titania has not been proved in this study, further experiments to show the necessity of direct contact between gold and titania for efficient reaction and thus existence of direct electron transfer from gold to titania are now in progress. To prove electron transfer from gold to titania, experiments using double-beam photoacoustic spectroscopy 54 with excitation of LSPR and detection of accumulated electrons will also be carried out.…”

Section: Discussionmentioning

confidence: 99%

Visible-light-induced photocatalysis through surface plasmon excitation of gold on titania surfaces

Kowalska

Mahaney

Abe

et al. 2010

Phys. Chem. Chem. Phys.

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Fifteen commercial titania (titanium(IV) oxide; TiO 2 ) powders were modified with gold by photodeposition to prepare photocatalysts that work under irradiation with light in the visible range (vis). The gold-modified titania (Au/TiO 2 ) powders were characterized by diffuse reflectance spectroscopy (DRS), field-emission scanning electron microscopy (FE-SEM), scanning transmission microscopy (STEM) and X-ray powder diffraction analysis (XRD). It was shown that all tested powders could absorb visible light with an absorption maximum at localized surface plasmon resonance (LSPR) wavelengths (530-600 nm) and that the size and shape of gold nanoparticles determined absorption ranges.The photocatalytic activity of Au/TiO 2 powders was examined both under ultraviolet and vis irradiation (mainly >450 nm) for acetic acid and 2-propanol photooxidation. It was found that the activity depended strongly on gold and titania properties, such as particle size and shape, surface area and crystalline form. Under vis irradiation, large rutile particles loaded with gold particles of a wide range of sizes showed the highest level of photocatalytic activity, possibly due to greater light absorption ability in a wide wavelength range resulting from transverse and longitudinal LSPR of rod-like gold particles. Action spectrum analyses showed that visible light-induced oxidation of organic compounds by aerated gold-titania suspensions was initiated by excitation of LSPR absorption of gold. Although photocatalytic activity of nanosized gold particles under vis irradiation with a wavelength of ca. 430 nm and catalytic activity of goldmodified titania during dark reaction were also found, it was shown that the activities of 2 Au/TiO 2 particles originated from activation of LSPR of gold by light of wavelength of 530-650 nm. Participation of molecular oxygen as an electron acceptor and titania as a conductor of electrons was suggested by comparison with results obtained under deaerated conditions and results obtained using a system containing gold-deposited silica instead of gold-titania, respectively. On the basis of these results, the mechanism of visible light-induced oxidation of organic compounds on gold-titania is proposed. IntroductionTitanium(IV) oxide (TiO 2 ; titania) is an inexpensive particulate material that is readily available and has substantial photocatalytic activity, stability toward inorganic and organic compounds and non-toxicity. 1 However, one drawback of titania is that it can only be excited by ultraviolet light, i.e., with wavelengths shorter than ca. 400 nm.Therefore, only a very small portion of solar radiation (3-5%) can be utilized to drive chemical reactions. 2 Thus, extension of its absorption wavelength range to the visible region (vis) is an important issue. Another important issue is improvement of quantum efficiency, i.e., an efficiency of utilization of the photoexcited state of photocatalysts, since an electronic excited state of titania is deactivated by recombination of electrons and holes to lower qu...

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Section: Discussionmentioning

confidence: 99%

Visible-light-induced photocatalysis through surface plasmon excitation of gold on titania surfaces

Kowalska

Mahaney

Abe

et al. 2010

Phys. Chem. Chem. Phys.

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517

419

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“…of WCA was independent of the wavelength and the mechanism could not be explained only by chemical reactions such as photocatalytic oxidative decomposition. Detailed and precise analyses of chemical composition and structure using, for example, double-beam photoacoustic spectroscopy (PAS) [14,15] before and during the course of photoirradiation are required for a full understanding of photoinduced hydrophilicity. …”

Section: Discussionmentioning

confidence: 99%

Action spectrum analyses of photoinduced superhydrophilicity of titania thin films on glass plates

et al. 2008

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Samples of titania-thin-film-coated glass plates were prepared by spin coating of commercial titania-coating liquids using a home-made spin coater (1000 rpm, 30 s) and then calcined in air at 673 K for 2 h. In a part of experiments, samples were stored in an oven at 393 K overnight. A piece of sample was set in a 10-mm rectangular quartz cell, and monochromatic light (FWHM of ca. 17 nm, intensity of ca. 10 8 einstein s -1 ) was irradiated in ambient air using a grating multiple-wavelength photoirradiation instrument (Jasco CRM-FD).Water contact angle (WCA) of samples before and after monochromatic irradiation was measured by a contact angle analyzer. Changes in WCA, as a function of wavelength of monochromatic irradiation, a kind of action spectrum, of several titania samples showed that the sample surfaces became superhydrophilic, i.e., WCA became almost zero, only under irradiation with a wavelength shorter than the absorption edge, corresponding to the band gap, of samples. Analysis of changes in WCA showed that there are at least two stages when the samples stored at 393 K overnight before irradiation to give relatively high WCA of ca. 40 deg. were used: first stage of WCA > 10 deg. and second stage of WCA < 10 deg.. The action spectra of WCA change in these two stages are discussed.

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“…One possible explanation is that OAP has preferred crystal lattice defects, which can be evaluated as electron traps working as a recombination center and a surface-adsorption site. The preliminary results of the measurement of such electron traps (ETs) by double-beam photoacoustic spectroscopy 15 showed that total ET density of the samples prepared with different US times was almost constant. It is expected that shallow and deep ETs in the band gap enhance the migration of electrons and recombination, respectively; thus, even if the total ET density is the same, the distribution of differences in the depth of ET may regulate the photocatalytic activity.…”

Section: ¹1mentioning

confidence: 99%

Enhanced Photocatalytic Activity by Particle Morphology: Preparation, Characterization, and Photocatalytic Activities of Octahedral Anatase Titania Particles

2013

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Titania samples containing octahedral anatase particles (OAPs) were prepared by the ultrasonicationhydrothermal process of partially proton-exchanged potassium titanate nanowires. It was found that increase in the ultrasonication time changed the product morphology, with other structural properties such as specific surface area, crystalline size, and crystallinity remaining almost constant. The results of photocatalytic activity tests for those samples suggested higher activity of a sample with higher OAP content, especially for reactions in the presence of oxygen.Titanium(IV) oxide (titania) has been used extensively for many years as a photocatalyst, mainly owing to its redox ability, stability, and nontoxicity.1,2 Though a large number of papers have been published on titania photocatalysis, the essence of its photocatalytic activity, e.g., the reason of various levels of photocatalytic activity of samples with various properties and polymorphic composition, has not been clarified. 3 Recently, crystallite morphology, which has been widely studied for reactions occurring on a titania single crystal (mainly rutile (110)) 4 but neglected for particulate photocatalysts, has been considered as one of the crucial factors affecting the photocatalytic activity of particulate titania on the basis of the results of studies performed using facetted octahedral 57 and decahedral 810 anatase particles. We have recently developed an ultrasonication (US)hydrothermal reaction (HT) process 11 to prepare octahedral anatase particles (OAPs), exposing eight themodynamically most stable equivalent {101} facets, with enhanced photocatalytic activity, especially for the oxidation of acetic acid in aerated aqueous solutions, compared with many commercial titania samples with similar properties. However, proof of higher activity only owing to OAP morphology has not yet been obtained, because particles with the same structural properties except for morphology could not be prepared. In order to prove the effect of particle morphology on the photocatalytic activity, we examined various preparation conditions. In this paper, we present the results of sample preparation using different OAP contents and with other structural properties that remain almost constant; we also show a comparison of their photocatalytic activities.The samples were fabricated by the USHT process (for details, see SI)12 using partially proton-exchanged potassium titanate nanowires (TNW; Earthclean Tohoku Co., Ltd.) prepared by the HT reaction of Evonik P25 (Nippon Aerosil) in a potassium hydroxide solution (17 mol L ¹1) at 383 K for 20 h, followed by washing with dilute hydrochloric acid. 13 The controlled parameters were the US time (04 h), HT reaction time (348 h), and HT temperature (413473 K). The products were collected by centrifugation and vacuum dried (353 K, 12 h).Specific surface areas of the products were estimated by nitrogen adsorption at 77 K using the BrunauerEmmettTeller (BET) equation. Crystallinity (anatase content) as well as crystallite size and ...

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Double-Beam Photoacoustic Spectroscopic Studies on Transient Absorption of Titanium(IV) Oxide Photocatalyst Powders

Cited by 87 publications

References 51 publications

Visible-light-induced photocatalysis through surface plasmon excitation of gold on titania surfaces

Visible-light-induced photocatalysis through surface plasmon excitation of gold on titania surfaces

Action spectrum analyses of photoinduced superhydrophilicity of titania thin films on glass plates

Enhanced Photocatalytic Activity by Particle Morphology: Preparation, Characterization, and Photocatalytic Activities of Octahedral Anatase Titania Particles

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