Colloidal TiO<sub>2</sub>particles as oxygen carriers in photochemical water cleavage systems

Duonghong, Dung; Grätzel, Michaël

doi:10.1039/c39840001597

Cited by 47 publications

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“…To determine any peroxides formed in the reaction, nanosheets were titrated with the redox indicator o-tolidine in the presence of colloidal Pt as a catalyst, as described previously. 11,18,20 The reaction at pH > 3 initially leads to a quinone-diimine complex (Supporting Information) with an absorbance maximum at 625 nm corresponding to a blue color. When o-tolidine is added to a suspension of catalyst (pH ) 10.5) that had been irradiated for 6 h, this blue color develops within 30 s. Nonirradiated samples do not show the blue color, and neither does the supernatant of irradiated samples after removal of the catalyst.…”

Section: Resultsmentioning

confidence: 99%

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Niobate Nanosheets as Catalysts for Photochemical Water Splitting into Hydrogen and Hydrogen Peroxide

2008

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Tetrabutylammonium-stabilized Ca 2 Nb 3 O 10 nanosheets catalyze photochemical splitting of water into hydrogen and hydrogen peroxide under UV irradiation. The peroxide forms on the surface of the catalyst and adsorbs to it, fully deactivating the catalyst after 48 h of irradiation. For the Pt-modified niobate, complete deactivation occurs within 24 h due to higher H 2 evolution rate with this system. The peroxide was identified via Raman and IR spectroscopy. In vibrational spectra, the irradiated niobate exhibits bands at 580, 778, and 940 cm -1 , which suggest that the peroxide is present as a side-on ligand coordinated to the Nb 5+ ions on the nanosheet surface. The same species can be formed by treating the nanosheets with 30% aqueous H 2 O 2 . If the catalyst is irradiated in H 2 18 O, the bands shift to lower energy, indicating that the peroxide species is formed from water. Room-temperature storage of the nanosheets in H 2 18 O also leads to isotopic exchange of all Nb-O atoms over the course of 24 h. Peroxide amounts measured by titration of the catalyst with o-tolidine after 6, 12, and 24 h of irradiation form in a 1:1 stoichiometry with hydrogen. Infrared data shows that the peroxide is partially desorbed by evacuating the catalyst and by purging with argon gas. Under catalytic conditions, this treatment restores up to 60% of the original activity. For the H 2 O 2 -treated catalyst, near quantitative H 2 O 2 desorption occurs within 20 min at 450°C. Separate irradiation experiments of the catalyst in the presence of air reveal that H 2 evolution is diminished and that O 2 uptake occurs from the atmosphere. Most of the hydrogen peroxide formed under these conditions is subsequently detected in the supernatant and only small amounts on the catalyst. NMR spectra show that the tetrabutylammonium cations are decomposed. These findings suggest that there are two distinct pathways for peroxide formation, one involving one-electron reduction of O 2 and one involving two-electron reduction of water (in the absence of O 2 ).

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Section: Resultsmentioning

confidence: 99%

“…If the band gap of the material is large enough (at least 2.4 eV), 6,7 irradiation of an aqueous catalyst dispersion can lead to H 2 and O 2 . However, for many metal oxides, including the anatase form of TiO 2 , [8][9][10][11] several titanates, and niobates (KCa 2 …”

Section: Introductionmentioning

confidence: 99%

Niobate Nanosheets as Catalysts for Photochemical Water Splitting into Hydrogen and Hydrogen Peroxide

2008

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“…The photocatalytic direct decomposition of water to hydrogen and oxygen is very attractive in terms of photo-energy conversion [9][10][11][12][13][14][15][16][17][18]. It is well-known that titanium oxide has highly photocatalytic activities in several photocatalytic reactions [11][12][13][14][15][16][17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

“…It is well-known that titanium oxide has highly photocatalytic activities in several photocatalytic reactions [11][12][13][14][15][16][17][18][19][20][21][22]. Metal-loaded titanium oxide photocatalysts, such as Pt/TiO 2 , can easily produce hydrogen for the photocatalytic direct decomposition of water in the presence of a reducing reagent, such as alcohols or formic acid [16][17][18], whereas it is known that light irradiation to titanium oxide itself in the absence of a reducing reagent cannot lead to water decomposition.…”

Section: Introductionmentioning

confidence: 99%

Photodecomposition of water with methane over titanium oxide photocatalysts modified with metal

et al. 2010

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Metal-loaded titanium oxide photocatalysts produced hydrogen in the photodecomposition of water vapor with methane in the flow reactor. Ag/TiO 2 has the highest activity in comparison with other metal-loaded catalysts. The experiment in the absence of methane indicated that methane could effectively function as a reducing reagent of water. The significant decrease in the hydrogen formation rate with the time on stream was observed under all reaction conditions. The recalcination and the hydrogen rereduction of the used catalyst led to the restoration of the activity of the hydrogen formation. The adsorption of products and/or reactants on the catalyst surface seemed to cause these deactivations of the hydrogen formation.

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“…Study of the macrodispersion of semiconductor powders in these systems is restricted by their intense turbidity, making it impossible to study transient species by fast kinetics spectroscopy (14,15). A study of the kinetics of electron transfer through the colloidal semiconductor/electrolyte solution interface is reported.…”

Section: Introductionmentioning

confidence: 99%

Interfase Óxido/Electrolito: Fenómeno de transferencia de electrones

Fernández‐Ibáñez¹,

Malato²,

Nieves³

2000

Bol. Soc. Esp. Ceram. Vidr.

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Electron transfer on a titanium dioxide/electrolyte solution interface has been studied. As observed by other researchers on similar interfaces (TiO 2 -and ZnO-electrolyte solution), slow consumption of OH -ions was found. A theoretical model has been developed for calculating the change in Fermi energy levels of both electrolyte solution and semiconductor, showing that ion consumption from the solution is favoured by a decreased difference in their Fermi energies. A kinetic constant (υ) is found to characterise the consumption process, its value increasing with electrolyte and semiconductor mass concentrations. Furthermore, this process may be used to estimate the point of zero charge of a titanium dioxide colloidal dispersion. Keywords: Titanium dioxide, Fermi level, point of zero charge, electrophoretic mobility.Interfase Óxido/Electrolito: Fenómeno de transferencia de electrones.En este trabajo se ha estudiado un proceso de transferencia de electrones en la interfase dióxido de titanio/electrolito acuoso. Tal y como han observado otros investigadores en interfases similares (TiO 2 -y ZnO-electrolito), se ha detectado un consumo lento de iones OH -. Para dar explicación a este proceso, se ha desarrollado un modelo teórico basado en el cálculo de las energías de Fermi en el semiconductor y en el electrolito. De este modo, se demuestra que dicho consumo de iones está favorecido por una disminución de la diferencia entre ambos niveles de Fermi. Para caracterizar el proceso de consumo lento de OH -se define una constante cinética (υ), cuyo valor aumenta a medida que crece la concentración másica de semiconductor y de electrolito en la suspensión. Adicionalmente, este fenómeno proporciona una herramienta para determinar experimentalmente el punto de carga nula de la suspensión de dióxido de titanio en el medio acuoso.Palabras clave: Dióxido de titanio, nivel de Fermi, punto de carga nula, movilidad electroforética.

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Colloidal TiO₂particles as oxygen carriers in photochemical water cleavage systems

Abstract: By using the redox indicators o-dianisidine and o-toluidine as reagents for quantitative analysis, it is shown that in colloidal Ti02-Pt dispersions surface-bound peroxo titanium complexes are formed during photolytic water cleavage in closed systems and as a result of oxygen photo-uptake.

Cited by 47 publications

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Niobate Nanosheets as Catalysts for Photochemical Water Splitting into Hydrogen and Hydrogen Peroxide

Niobate Nanosheets as Catalysts for Photochemical Water Splitting into Hydrogen and Hydrogen Peroxide

Photodecomposition of water with methane over titanium oxide photocatalysts modified with metal

Interfase Óxido/Electrolito: Fenómeno de transferencia de electrones

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Colloidal TiO2particles as oxygen carriers in photochemical water cleavage systems

Cited by 47 publications

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Niobate Nanosheets as Catalysts for Photochemical Water Splitting into Hydrogen and Hydrogen Peroxide

Niobate Nanosheets as Catalysts for Photochemical Water Splitting into Hydrogen and Hydrogen Peroxide

Photodecomposition of water with methane over titanium oxide photocatalysts modified with metal

Interfase Óxido/Electrolito: Fenómeno de transferencia de electrones

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Colloidal TiO₂particles as oxygen carriers in photochemical water cleavage systems