Surface Science Studies of the Photoactivation of TiO<sub>2</sub>New Photochemical Processes

Thompson, Tracy; Yates, John T.

doi:10.1021/cr050172k

Cited by 1,994 publications

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“…ABSTRACT: It is well established that adding methanol to water could significantly enhance H 2 production by TiO 2 . Recently, we have found that methanol can be photocatalytically dissociated on TiO 2 (110) at 400 nm via a stepwise mechanism.…”

Section: * S Supporting Informationmentioning

confidence: 99%

“…In this work, we have investigated deuterium formation from photocatalysis of the fully deuterated methanol (CD 3 OD) on TiO 2 (110) at 400 nm using a temperature programmed desorption (TPD) technique. Photocatalytic dissociation products formaldehyde (CD 2 T iO 2 has attracted enormous interest in heterogeneous catalysis, photocatalysis, solar energy devices, etc. 1−8 Photocatalytic water splitting by TiO 2 is especially attractive because of its potential application in clean hydrogen production.…”

Section: * S Supporting Informationmentioning

confidence: 99%

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Molecular Hydrogen Formation from Photocatalysis of Methanol on TiO₂(110)

et al. 2013

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It is well established that adding methanol to water could significantly enhance H 2 production by TiO 2 . Recently, we have found that methanol can be photocatalytically dissociated on TiO 2 (110) at 400 nm via a stepwise mechanism. However, how molecular hydrogen can be formed from the photocatalyzed methanol/ TiO 2 (110) surface is still not clear. In this work, we have investigated deuterium formation from photocatalysis of the fully deuterated methanol (CD 3 OD) on TiO 2 (110) at 400 nm using a temperature programmed desorption (TPD) T iO 2 has attracted enormous interest in heterogeneous catalysis, photocatalysis, solar energy devices, etc. 1−8 Photocatalytic water splitting by TiO 2 is especially attractive because of its potential application in clean hydrogen production. 9 A previous study found that pure TiO 2 is not active for hydrogen production from pure water. 10 Adding methanol to pure water, however, can dramatically enhance hydrogen production. 11 Because of the apparently crucial role in hydrogen production, the photochemistry of methanol has been extensively investigated on single crystal TiO 2 surfaces 12−31 and TiO 2 powders. 32−35 Although investigations on powder TiO 2 with methanol steam 32−35 and a water−methanol mixture 11 show that hydrogen can be produced from methanol by reaction,the detailed mechanism of gaseous hydrogen formation from methanol photocatalysis on TiO 2 remains unknown. In a recent study, 28 we have shown that the elementary photocatalytic dissociation of CH 3 OH on TiO 2 (110) without any other coadsorbed species occurs in a stepwise mechanism in which the O−H dissociation proceeds first and is then followed by C−H dissociation to form formaldehyde (CH 2 O) with only methanol adsorption on TiO 2 (110),where Ti 5C refers to a five-coordinated Ti 4+ (Ti 5C ) site, and H BBO refers to an H atom adsorbed on a bridge-bonded oxygen (BBO) site on the TiO 2 (110) surface. From our experiment, we have found that both dissociation steps are photoinitiated. This means that at low temperature photocatalytic dissociation products from CH 3 OH, i.e., CH 2 O and H atoms on BBO sites, are all left on the TiO 2 surface after laser irradiation, whereas Henderson and co-workers found that molecular CH 3 OH is not photoactive on TiO 2 (110) using a Hg lamp as the surface photocatalysis source. 26 In our experiment, 28,36 we used a femtosecond laser source that has considerably higher photon flux than the Hg lamp used in ref 26, in addition to the highly sensitive mass spectrometric detector with a vacuum background of 1 × 10 −12 Torr. We believe this makes our experiment much more sensitive in detecting TPD products. Further oxidation of CH 3 OH on TiO 2 (110) to form methyl formate has also been observed in three different laboratories. 36−38 However, the important question of how hydrogen molecules are formed from the photocatalysis of methanol on TiO 2 (110) remains unanswered. In order to understand the mechanism of hydrogen formation, the photocatalytic chemistry of CD ...

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Section: * S Supporting Informationmentioning

confidence: 99%

Section: * S Supporting Informationmentioning

confidence: 99%

Molecular Hydrogen Formation from Photocatalysis of Methanol on TiO₂(110)

et al. 2013

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“…A particular important example is titanium oxide which is used in catalysis and photocatalysis [1,2], as white pigment, in sun blockers, and also in solar technologies [3][4][5]. An important part of the Grätzel-cell, a dye-sensitized device for the conversion of sunlight into electrical energy (DSSC) first reported in 1991, is a mesoporous oxide layer (TiO 2 , SnO 2 , ZnO) [3].…”

Section: Introductionmentioning

confidence: 99%

Interaction of carboxylic acids with rutile TiO2(110): IR-investigations of terephthalic and benzoic acid adsorbed on a single crystal substrate

Buchholz

Noei

et al. 2016

Surface Science

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a b s t r a c t a r t i c l e i n f oThe adsorption of two carboxylic acids, benzoic acid (BA) and terephthalic acid (TPA), on a single crystal rutile TiO 2 (110) substrate was studied using infrared reflection-absorption spectroscopy (IRRAS) in conjunction with DFT calculations. On the basis of the high-quality IR data (in particular for the OH bands), various adsorbate species with different geometries could be identified. The adsorption of both, BA and TPA, on TiO 2 (110) leads to deprotonation of carboxylic acids and protonation of substrate O-atoms. At low coverage, the deprotonated BA molecule adsorbs on TiO 2 (110) in an upright, bidentate configuration, while the TPA molecule adopts a flatlying geometry with both carboxylates bound to the surface in a monodentate geometry. At higher coverages, a transition from flat-lying to upright-oriented TPA molecules occurs. At saturation coverage, both BA and TPA molecules undergo dimerization indicating the presence of pronounced attractive intermolecular interactions. We propose that the BA dimers are stabilized by the interaction between adjacent phenyl rings, while the TPA dimerization is attributed to the formation of double hydrogen bonds between adjacent apical carboxylic groups.

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“…8 The electronic structure of bulk TiO 2 is now well understood, [7][8] whereas the structure and properties of the surface remain controversial. [8][9] The TiO 2 surface consists of high-energy bond configurations in which the terminal Ti and O atoms rearrange so that the symmetry and electronic structure of the resulting surface is different from that of the bulk 10 creating states that would be considered defects in the bulk material. These defect states are composed of undercoordinated Ti 4+ sites resulting from surface curvature, and oxygen vacancies resulting in Ti 3+ sites.…”

Section: Introductionmentioning

confidence: 99%

Controlling Surface Defects and Photophysics in TiO₂ Nanoparticles

et al. 2014

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Titanium dioxide (TiO 2 ) is widely used for photocatalysis and solar cell applications, and the electronic structure of bulk TiO 2 is well understood. However, surface structure of nanoparticulate TiO 2 , which has a key role in properties such as solubility and catalytic activity, still remains controversial. Detailed understanding of surface defects structures may help explain reactivity and overall materials performance in a wide range of applications. In this work we address the solubility problem and surface defects control on TiO 2 nanoparticles. We report the synthesis and characterization of ~ 4 nm TiO 2 anatase spherical nanoparticles that are soluble and stable in a wide range of organic solvents and water. By controlling the temperature during the synthesis, we are able to tailor the density of defect states on the surface of the TiO 2 nanoparticles without affecting parameters such as size, shape, core crystallinity and solubility.The morphology of both kinds of nanoparticles was determined by TEM. EPR experiments were used to characterize the surface defects, and transient absorption measurements demonstrate the influence of the TiO 2 defect states on photoinduced electron transfer dynamics.3

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Surface Science Studies of the Photoactivation of TiO₂New Photochemical Processes

Cited by 1,994 publications

References 140 publications

Molecular Hydrogen Formation from Photocatalysis of Methanol on TiO₂(110)

Molecular Hydrogen Formation from Photocatalysis of Methanol on TiO₂(110)

Interaction of carboxylic acids with rutile TiO2(110): IR-investigations of terephthalic and benzoic acid adsorbed on a single crystal substrate

Controlling Surface Defects and Photophysics in TiO₂ Nanoparticles

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Surface Science Studies of the Photoactivation of TiO2New Photochemical Processes

Cited by 1,994 publications

References 140 publications

Molecular Hydrogen Formation from Photocatalysis of Methanol on TiO2(110)

Molecular Hydrogen Formation from Photocatalysis of Methanol on TiO2(110)

Interaction of carboxylic acids with rutile TiO2(110): IR-investigations of terephthalic and benzoic acid adsorbed on a single crystal substrate

Controlling Surface Defects and Photophysics in TiO2 Nanoparticles

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Surface Science Studies of the Photoactivation of TiO₂New Photochemical Processes

Molecular Hydrogen Formation from Photocatalysis of Methanol on TiO₂(110)

Molecular Hydrogen Formation from Photocatalysis of Methanol on TiO₂(110)

Controlling Surface Defects and Photophysics in TiO₂ Nanoparticles