Catalytic photo-oxidation of cyclohexene by aqueous uranyl–polymolybdate(<scp>VI</scp>) systems

Mooney, William F.; Chauveau, F.; Tran‐Thi, T.‐H.; Folcher, G.; Giannotti, C.

doi:10.1039/p29880001479

Cited by 11 publications

(6 citation statements)

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“…Spin trapping of hydroxyl radicals has previously been reported on photolysis of aqueous uranyl solutions in the presence of polymolybdate() systems. 72 We should note that the observation of the ESR spectra of the radicals from spin adducts is not conclusive evidence for reaction (1) since quenching of excited uranyl ion by the spin traps may produce radical cations, which can themselves produce hydroxyl radicals 73 through the reactions (for the case of PBN):…”

Section: Spin Trapping Studies and Other Evidence For Formation Of Re...mentioning

confidence: 99%

Deactivation processes of the lowest excited state of [UO2(H2O)5]2+ in aqueous solution

Formosinho

Burrows

Miguel

et al. 2003

Photochem Photobiol Sci

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A detailed analysis of the photophysical behaviour of uranyl ion in aqueous solutions at room temperature is given using literature data, together with results of new experimental and theoretical studies to see whether the decay mechanism of the lowest excited state involves physical deactivation by energy transfer or a chemical process through hydrogen atom abstraction. Comparison of the radiative lifetimes determined from quantum yield and lifetime data with that obtained from the Einstein relationship strongly suggests that the emitting state is identical to that observed in the lowest energy absorption band. From study of the experimental rate and that calculated theoretically, from deuterium isotope effects and the activation energy for decay support is given to a deactivation mechanism of hydrogen abstraction involving water clusters to give uranium(v) and hydroxyl radicals. Support for hydroxyl radical formation comes from electron spin resonance spectra observed in the presence of the spin traps 5,5-dimethyl-1-pyrroline N-oxide and tert-butyl-N-phenylnitrone and from literature results on photoinduced uranyl oxygen exchange and photoconductivity. It has previously been suggested that the uranyl emission above pH 1.5 may involve an exciplex between excited uranyl ion and uranium(v). Evidence against this mechanism is given on the basis of quenching of uranyl luminescence by uranium(v), together with other kinetic reasoning. No overall photochemical reaction is observed on excitation of aqueous uranyl solutions, and it is suggested that this is mainly due to reoxidation of UO2+ by hydroxyl radicals in a radical pair. An alternative process involving oxidation by molecular oxygen is analysed experimentally and theoretically, and is suggested to be too slow to be a major reoxidation pathway.

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Section: Spin Trapping Studies and Other Evidence For Formation Of Re...mentioning

confidence: 99%

Deactivation processes of the lowest excited state of [UO2(H2O)5]2+ in aqueous solution

Formosinho

Burrows

Miguel

et al. 2003

Photochem Photobiol Sci

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“…It is well-known that oxygen vacancies exist in n-type semiconducting oxides acting as donors, which can enhance their sensor response as exposed to reductive gas. It has been found that amorphous semiconducting oxides could offer a strong gas response and fast responding/recovering speed due to their low density and high surface permeability compared with their corresponding crystalline materials . The sensor response of the C/A-C/S MoO 3 composite to 10–500 ppm ethanol at the working temperature ranging from 150 to 225 °C is shown in Figure a–c.…”

Section: Resultsmentioning

confidence: 99%

“…It has been found that amorphous semiconducting oxides could offer a strong gas response and fast responding/recovering speed due to their low density and high surface permeability compared with their corresponding crystalline materials. 56 The sensor response of the C/A-C/S MoO 3 composite to 10−500 ppm ethanol at the working temperature ranging from 150 to 225 °C is shown in Figure 3a−c. Through comparing the sensitivities to ethanol gas of the C/A-C/S MoO 3 composite working at 150, 180, and 225 °C, it is obvious that 180 °C is the most optimum working temperature, which is lower than the results reported in the previous literature.…”

Section: Crystal Growth and Designmentioning

confidence: 99%

“…63 Similarly, in this work, the ethanol sensing mechanism over α-MoO 3 is an ethanol's catalytic oxidation process. 56,64 The sensitivity action over the C/A-C/S of MoO 3 surface layer processes through reacting with dissociative adsorbed ethanol, as illustrated in eq 1. The O−H bond of the adsorbed ethanol dissociates heterolytically to yield ethoxide groups and hydrogen: 65,66 (1)…”

Section: Crystal Growth and Designmentioning

confidence: 99%

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Synthesis of Crystalline/Amorphous Core/Shell MoO₃ Composites through a Controlled Dehydration Route and Their Enhanced Ethanol Sensing Properties

Wang

Gao

Bao

et al. 2014

Crystal Growth & Design

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Considering the specific surface area, flexible structures, high porosity, and a homogeneous and isotropic nature down to the atomic scale possessed by the amorphous nanostructure, an interesting controlled dehydration route has been developed to synthesize the crystalline/ amorphous core/shell (C/A-C/S) MoO 3 nanocomposite, in which macroisopolyanion [Mo 36 O 112 (H 2 O) 16 ] 8− ({Mo 36 }) was successfully assembled into a one-dimensional connection and underwent a deficient crystallization induced by the prospective infiltrative dehydration process. The as-obtained MoO 3 samples' affirmative composition and composite structure have been further demonstrated by the XRD, TEM, HRTEM, and Raman spectra measurements. As a result of this special C/A-C/S structure, the MoO 3 composite exhibited high selectivity and a higher sensor response, at a lower working temperature (180 °C) to ethanol gas compared with other 1D MoO 3 micro/ nanostructures reported previously.

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“…Recent studies with the uranyl ion (UO 2 2+ ) have shown that it has the potential to photocatalytically oxidize organic substrates in the presence of air. − The excited-state UO 2 2+* is a potent oxidant ( E ° = 2.6 V), and is quenched by a variety of organic substrates. ,− The resulting U(V) species can then be oxidized back to UO 2 2+ in the presence of oxygen . Previous studies with alcohols have shown, through kinetic isotope effects, that the quenching of the uranyl excited state occurs by hydrogen atom abstraction to give UO 2 H + and an organic radical. ,, The mechanism of quenching with alkenes has not been definitively determined. − Proposals for quenching mechanisms with alkenes have included exciplex formation, H-atom abstraction, and electron transfer. Recent work identified a U(V) species as a quenching product in the absence of oxygen, and suggested H-atom abstraction as the quenching mechanism …”

Section: Introductionmentioning

confidence: 99%

Uranyl Photochemistry with Alkenes: Distinguishing between H-Atom Abstraction and Electron Transfer

1999

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We have studied the quenching of the uranyl ion in aqueous acetonitrile with a series of alkenes. The quenching rate constant (k q) increases linearly with decreasing ionization potential (IP) for a series of hexene isomers, as seen in a plot of ln(k q) vs IP; no correlation is observed between the quenching rate and the bond dissociation energy of the allylic C−H bond. These results demonstrate that the mechanism of quenching for alkenes is electron transfer from the alkene to uranyl.

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Catalytic photo-oxidation of cyclohexene by aqueous uranyl–polymolybdate(VI) systems

Cited by 11 publications

References 5 publications

Deactivation processes of the lowest excited state of [UO2(H2O)5]2+ in aqueous solution

Deactivation processes of the lowest excited state of [UO2(H2O)5]2+ in aqueous solution

Synthesis of Crystalline/Amorphous Core/Shell MoO₃ Composites through a Controlled Dehydration Route and Their Enhanced Ethanol Sensing Properties

Uranyl Photochemistry with Alkenes: Distinguishing between H-Atom Abstraction and Electron Transfer

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Catalytic photo-oxidation of cyclohexene by aqueous uranyl–polymolybdate(VI) systems

Cited by 11 publications

References 5 publications

Deactivation processes of the lowest excited state of [UO2(H2O)5]2+ in aqueous solution

Deactivation processes of the lowest excited state of [UO2(H2O)5]2+ in aqueous solution

Synthesis of Crystalline/Amorphous Core/Shell MoO3 Composites through a Controlled Dehydration Route and Their Enhanced Ethanol Sensing Properties

Uranyl Photochemistry with Alkenes: Distinguishing between H-Atom Abstraction and Electron Transfer

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Synthesis of Crystalline/Amorphous Core/Shell MoO₃ Composites through a Controlled Dehydration Route and Their Enhanced Ethanol Sensing Properties