Photocatalytic and photoelectrochemical oxidation mechanisms of methanol on TiO2 in aqueous solution

Ahmed, Amira Y.; Kandiel, Tarek A.; Ivanova, I. I.; Bahnemann, Detlef W.

doi:10.1016/j.apsusc.2014.07.134

Cited by 53 publications

(49 citation statements)

References 56 publications

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“…Moderate and similar average effects were observed with the change of type of electron donor (B) and its concentration (D), which increase the average response by 27 % (from 45 to 57 μmol) when methanol was replaced with ethanol and by 20 % (from 46 to 57 μmol) when its concentration increased from 1.2 to 2.2 m . This increase in alcohol concentration agrees with results published previously, in which hydrogen production was dependent on the alcohol concentration for diluted solutions up to 6–7 m and if the direct oxidation of alcohol molecules by photogenerated holes occurs at the TiO 2 surface with concentrations above 0.12 m (0.47 vol %) . Its influence is related to its sequential process and the lifetimes of the photogenerated electron–hole pairs.…”

Section: Resultssupporting

confidence: 92%

Operational Conditions Affecting Hydrogen Production by the Photoreforming of Organic Compounds using Titania Nanoparticles with Gold

et al. 2018

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Several factors affect photocatalytic hydrogen productivity from the photoreforming of organic compounds, which makes it difficult to optimize operational conditions in photoreactors. To prioritize these factors, we focused on the quantification of the effect of five of them on hydrogen production. Photocatalytic experiments were performed on 67 mL batch photoreactors under UV‐LED lamps (λ=375 nm) using a suspension of TiO2–Au nanoparticles synthesized by a sol–gel approach. The analyzed factors were: (A) presence of Au as a cocatalyst, (B) type of alcohol as the electron donor, (C) intensity of UV light, (D) electron donor concentration, and (E) nanoparticle concentration. A main and interaction effects analysis is presented with reduced fixed effect models for three responses: total hydrogen generation, catalyst productivity, and electron donor productivity. The presence of Au as a cocatalyst (A), the intensity of UV light (C), and their interaction (AC) were the factors with the highest effect. The best configuration allowed us to reach a catalyst productivity of 2925 μmolnormalH2 g−1 h−1.

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Section: Resultssupporting

confidence: 92%

Operational Conditions Affecting Hydrogen Production by the Photoreforming of Organic Compounds using Titania Nanoparticles with Gold

et al. 2018

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“…Phillips et al report that for R-TiO 2 the photo-dissociation of a surface methoxy group to produce formaldehyde (reaction 2) is a direct hole-mediated reaction and is the rate limiting step for this process. 26 Indirect pathways involving photochemically produced hydroxyl radicals can also occur, especially in aqueous environments, 44,45 but are not likely to play an important role for the UHV conditions used in the present study. 30 While this mechanism is consistent with reaction on the exposed (101) surfaces of the nanocrystals, the results obtained in the present study exhibit some features that were not observed in a previous study by Xu et al of the photo-oxidation of methanol on A-TiO 2 (101).…”

Section: Discussionmentioning

confidence: 96%

Thermal and photochemical reactions of methanol on nanocrystalline anatase TiO₂thin films

Bennett

Cargnello

Gordon

et al. 2015

Phys. Chem. Chem. Phys.

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The catalytic and photo-catalytic activity of well-defined anatase TiO2 nanocrystals for the partial oxidation of methanol was investigated using temperature-programmed desorption (TPD) in ultra-high vacuum in order to determine how crystallite size and shape affect reactivity. The TiO2 films used in this study were prepared from well-defined TiO2 nanocrystals synthesized by colloidal methods. These nanocrystals had a truncated bi-pyramidal shape which exposes primarily (101) and to a lesser extent (001) surfaces and ranged in size from 10 to 25 nm. Two distinct regimes of reactivity were investigated, namely in the dark and under UV light illumination. In the dark, methanol adsorbed dissociatively on the (001) planes and only molecularly on the (101) surfaces. Dissociated methoxy groups on the (001) surfaces coupled to produce dimethyl ether, suggesting the presence of fourfold coordinate Ti cations. Under UV light illumination, the nanocrystals were additionally found to be active for the photo-catalytic oxidation of methanol to methyl formate. On the (101) surfaces, this reaction proceeded in a stepwise photocatalytic pathway involving dehydrogenation of methanol to form methoxy groups and then formaldehyde, followed by coupling of these latter two species to form methyl formate. The (001) surfaces were also found to be photo-catalytically active but surface methoxy groups could be produced thermally and the reaction proceeds only to formaldehyde in the absence of molecularly adsorbed methanol. The overall photocatalytic activity of the nanocrystals was also was found to increase with increasing crystallite size. The results of this study show that thin films of well-defined nanocrystals are excellent model systems that can be used to help bridge the materials gap between studies of single crystal surfaces and high surface area polycrystalline catalysts.

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“…All these processes involve the transfer of photogenerated holes to adsorbed species or the indirect transfer to an adsorbed water molecule yielding • OH radicals at the surface, which will further oxidize the substrate molecules 65 . The performance of the photocatalyst prepared via hydrothermal treatment was even better than that observed for the commercial photocatalyst P25 for methanol oxidation.…”

Section: Discussionmentioning

confidence: 99%

Charge carrier dynamics and photocatalytic behavior of TiO₂ nanopowders submitted to hydrothermal or conventional heat treatment

et al. 2015

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The sol-gel technique followed by conventional (TiO 2 -1) and hydrothermal (TiO 2 -2) thermal treatment was employed to prepare TiO 2 -based photocatalysts with distinct particle sizes and crystalline structures. The as prepared metal oxides were evaluated as photocatalysts for gaseous HCHO degradation, methanol, and dye oxidation reactions. Additionally, metallic platinum was deposited on the TiO 2 surfaces and H 2 evolution measurements were performed. The photocatalytic activities were rationalized in terms of morphologic parameters along with the electron/hole dynamics obtained from transient absorption spectroscopy (TAS).TiO 2 -2 exhibits smaller particle size, poorer crystallinity, and higher surface area than TiO 2 -1. Moreover the hydrothermal treatment leads to formation of the metastable brookite phase, while TiO 2 -1 exhibits only the anatase phase. TAS measurements show that the electron/hole recombination of TiO 2 -2 is faster than that of the later. Despite of that, TiO 2 -2 exhibits higher photonic efficiencies for photocatalytic oxidation reactions, which is attributed to its larger surface area that compensates the decrease of the surface charge carrier concentration. For H 2 evolution, it was found that the surface area has only a minor effect and the photocatalyst performance is controlled by the efficiency of the electron transfer to the platinum islands. This process is facilitated by the higher crystallinity of TiO 2 -1, which exhibits higher photonic efficiency for H 2 evolution than that observed for TiO 2 -2. The results found here provide new insights into the correlations between thermal treatment conditions and photocatalytic activity and will be useful for the design of high performance photocatalysts.

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Photocatalytic and photoelectrochemical oxidation mechanisms of methanol on TiO2 in aqueous solution

Cited by 53 publications

References 56 publications

Operational Conditions Affecting Hydrogen Production by the Photoreforming of Organic Compounds using Titania Nanoparticles with Gold

Operational Conditions Affecting Hydrogen Production by the Photoreforming of Organic Compounds using Titania Nanoparticles with Gold

Thermal and photochemical reactions of methanol on nanocrystalline anatase TiO₂thin films

Charge carrier dynamics and photocatalytic behavior of TiO₂ nanopowders submitted to hydrothermal or conventional heat treatment

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Photocatalytic and photoelectrochemical oxidation mechanisms of methanol on TiO2 in aqueous solution

Cited by 53 publications

References 56 publications

Operational Conditions Affecting Hydrogen Production by the Photoreforming of Organic Compounds using Titania Nanoparticles with Gold

Operational Conditions Affecting Hydrogen Production by the Photoreforming of Organic Compounds using Titania Nanoparticles with Gold

Thermal and photochemical reactions of methanol on nanocrystalline anatase TiO2thin films

Charge carrier dynamics and photocatalytic behavior of TiO2 nanopowders submitted to hydrothermal or conventional heat treatment

Contact Info

Product

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Thermal and photochemical reactions of methanol on nanocrystalline anatase TiO₂thin films

Charge carrier dynamics and photocatalytic behavior of TiO₂ nanopowders submitted to hydrothermal or conventional heat treatment