Heteropolyacid-based materials as heterogeneous photocatalysts

Heteropolyacids (HPAs) that are often used as heteropolyanions are cheap and stable compounds that have been extensively used as acid and oxidation catalysts as a result of their strong Brønsted acidity and ability to undergo multielectron-transfer reactions. HPAs, which are very soluble in water and polar solvents, have been also used as homogeneous photocatalysts for the oxidation of organic substrates in the presence of oxygen, but their use in heterogeneous systems is by far desirable. Dispersing HPAs onto solid supports with high surface area is useful to increase their specific surface area and hence (photo)catalytic activity. Moreover, owing to the high energy gap between the HOMO and LUMO positions of the HPAs, these compounds are activated only by UV light. Consequently, only less than 5 % of the solar light can be used in photocatalytic reactions, which restricts the practical application of HPAs. This microreview is oriented to describe the reported literature on the use of HPA-based materials as heterogeneous photocatalysts for environmental purposes, that is, for the complete or partial oxidation or reduction of organic molecules

Polyoxométallates et chimie verte : molécules et matériaux nanostructurés pour la conversion de l’énergie et l’environnement

This thesis focuses on the synthesis of nanostructured composite materials based on polyoxometalates for energy conversion and applications to environmental problems. To achieve these goals, many new compounds of this family of molecular oxides were synthesized and were associated with different nature friendly matrices, in agreement with the main criteria of Green Chemistry. In the field of energy, the new catalysts have proved very effective in important but difficult to achieve reactions, such as producing hydrogen, oxygen reduction or water oxidation. Similarly, among applications to pollution problems, these nanomaterials have shown a strong electrocatalytic and photocatalytic activity for the reduction of nitrogen oxides, bromate and for the photodegradation of a toxic textile dye, Acid Orange 7. The performances of these new catalysts are comparable to those of the best known systems.Ce mémoire porte sur la synthèse de matériaux composites nanostructurés à base de polyoxométallates pour la conversion de l’énergie et des applications à des problèmes environnementaux. Pour atteindre ces objectifs, de nombreux composés nouveaux de cette famille d’oxydes moléculaires ont été synthétisés puis ont été associés à différentes matrices éco-compatibles dans le respect des principaux critères de la Chimie Verte. Les principales techniques d’étude sont l’électrochimie, la photochimie et la spectroscopie UV-visible. Dans le domaine de l’énergie, les catalyseurs obtenus se sont révélés très efficaces dans des réactions très importantes mais difficiles à réaliser, comme la production de l’hydrogène, la réduction de l’oxygène et l’oxydation de l’eau. De même, parmi les applications aux problèmes de dépollution, ces nanomatériaux ont montré une forte activité électrocatalytique et photocatalytique pour la réduction des oxydes d’azote, des bromates et la photodégradation d’un colorant textile toxique, l’Acide Orange 7. Les performances de ces nouveaux catalyseurs sont comparables à celles des meilleurs systèmes connus

Polyoxometalates and green chemistry : nanostructured composite molecules and materials based on polyoxometalates for energy conversion and environment

Ce mémoire porte sur la synthèse de matériaux composites nanostructurés à base de polyoxométallates pour la conversion de l’énergie et des applications à des problèmes environnementaux. Pour atteindre ces objectifs, de nombreux composés nouveaux de cette famille d’oxydes moléculaires ont été synthétisés puis ont été associés à différentes matrices éco-compatibles dans le respect des principaux critères de la Chimie Verte. Les principales techniques d’étude sont l’électrochimie, la photochimie et la spectroscopie UV-visible. Dans le domaine de l’énergie, les catalyseurs obtenus se sont révélés très efficaces dans des réactions très importantes mais difficiles à réaliser, comme la production de l’hydrogène, la réduction de l’oxygène et l’oxydation de l’eau. De même, parmi les applications aux problèmes de dépollution, ces nanomatériaux ont montré une forte activité électrocatalytique et photocatalytique pour la réduction des oxydes d’azote, des bromates et la photodégradation d’un colorant textile toxique, l’Acide Orange 7. Les performances de ces nouveaux catalyseurs sont comparables à celles des meilleurs systèmes connus.This thesis focuses on the synthesis of nanostructured composite materials based on polyoxometalates for energy conversion and applications to environmental problems. To achieve these goals, many new compounds of this family of molecular oxides were synthesized and were associated with different nature friendly matrices, in agreement with the main criteria of Green Chemistry. In the field of energy, the new catalysts have proved very effective in important but difficult to achieve reactions, such as producing hydrogen, oxygen reduction or water oxidation. Similarly, among applications to pollution problems, these nanomaterials have shown a strong electrocatalytic and photocatalytic activity for the reduction of nitrogen oxides, bromate and for the photodegradation of a toxic textile dye, Acid Orange 7. The performances of these new catalysts are comparable to those of the best known systems

Polyoxométallates et chimie verte : molécules et matériaux nanostructurés pour la conversion de l’énergie et l’environnement

This thesis focuses on the synthesis of nanostructured composite materials based on polyoxometalates for energy conversion and applications to environmental problems. To achieve these goals, many new compounds of this family of molecular oxides were synthesized and were associated with different nature friendly matrices, in agreement with the main criteria of Green Chemistry. In the field of energy, the new catalysts have proved very effective in important but difficult to achieve reactions, such as producing hydrogen, oxygen reduction or water oxidation. Similarly, among applications to pollution problems, these nanomaterials have shown a strong electrocatalytic and photocatalytic activity for the reduction of nitrogen oxides, bromate and for the photodegradation of a toxic textile dye, Acid Orange 7. The performances of these new catalysts are comparable to those of the best known systems.Ce mémoire porte sur la synthèse de matériaux composites nanostructurés à base de polyoxométallates pour la conversion de l’énergie et des applications à des problèmes environnementaux. Pour atteindre ces objectifs, de nombreux composés nouveaux de cette famille d’oxydes moléculaires ont été synthétisés puis ont été associés à différentes matrices éco-compatibles dans le respect des principaux critères de la Chimie Verte. Les principales techniques d’étude sont l’électrochimie, la photochimie et la spectroscopie UV-visible. Dans le domaine de l’énergie, les catalyseurs obtenus se sont révélés très efficaces dans des réactions très importantes mais difficiles à réaliser, comme la production de l’hydrogène, la réduction de l’oxygène et l’oxydation de l’eau. De même, parmi les applications aux problèmes de dépollution, ces nanomatériaux ont montré une forte activité électrocatalytique et photocatalytique pour la réduction des oxydes d’azote, des bromates et la photodégradation d’un colorant textile toxique, l’Acide Orange 7. Les performances de ces nouveaux catalyseurs sont comparables à celles des meilleurs systèmes connus

Gas-phase protonation thermochemistry of glutamic acid.

International audienceProton affinity, PA(Glu), and protonation entropy (i.e., the difference Delta(p)S(o)(Glu) = S(o)(GluH(+)) - S(o)(Glu)) of glutamic acid have been experimentally determined by the extended kinetic method using electrospray ionization triple quadrupole-time-of-flight (ESI-Q-TOF) tandem mass spectrometry. The values deduced from these experiments are PA(Glu) = 945.3 +/- 2.8(5.8) kJ x mol(-1) and Delta(p)S(o)(Glu) = -28 +/- 4(9) J x mol(-1) x K(-1) thus leading to a gas-phase basicity, GB(Glu), of 904.4 +/- 3.0(6.4) kJ x mol(-1) (uncertainties are standard deviation and, in parentheses, 95% confidence limit). Theoretical calculations performed at the G3MP2B3 level provide information on the structures, conformations, and energetics of the neutral and protonated species. Thermochemical data are calculated at this level and include a correction to the computation of the entropy associated with hindered rotation. When the lowest energy conformers of protonated and neutral glutamic acid are considered the following values are calculated: PA(Glu) = 948.1 kJ x mol(-1) and Delta(p)S(o)(Glu) = -31.3 J x mol(-1) x K(-1). Using G3MP2B3 data to estimate the gas-phase distribution of conformers at 298 K, the averaged molar quantities becomes PA(Glu) = 949.8 kJ x mol(-1) and Delta(p)S(o)(Glu) = -36.0 J x mol(-1) x K(-1). Both computations give comparable GB(Glu) = 906.4-906.7 kJ x mol(-1)

Gas-phase protonation thermochemistry of arginine.

International audienceThe gas-phase basicity (GB), proton affinity (PA), and protonation entropy (DeltapS degrees (M)=S degrees (MH+)-S degrees (M)) of arginine (Arg) have been experimentally determined by the extended kinetic method using an electrospray ionization quadrupole time-of-flight (ESI-Q-TOF) mass spectrometer. This method provides GB(Arg)=1004.3+/-2.2 (4.9) kJ.mol(-1) (indicated errors are standard deviations, and in parentheses, 95% confidence limits are given). Consideration of previous experimental data using a fast atom bombardment ionization tandem sector mass spectrometer slightly modifies these estimates since GB(Arg)=1005.9+/-3.1 (6.6) kJ.mol(-1). Lower limits of the proton affinity, PA(Arg)=1046+/-4 (7) kJ.mol(-1), and of the "protonation entropy", DeltapS degrees (Arg)=S degrees (ArgH+)-S degrees (Arg)=-27+/-7 (15) J.mol(-1).K(-1), are also provided by the experiments. Theoretical calculations conducted at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d,p) level, including 298 K enthalpy correction, predict a proton affinity value of ca. 1053 kJ.mol-1 after consideration of isodesmic proton-transfer reactions with guanidine as the reference base. Computations including explicit treatment of hindered rotations and mixing of conformers confirm that a noticeable entropy loss does occur upon protonation, which leads to a theoretical DeltapS degrees (Arg) term of ca. -45 J.mol(-1).K(-1). The following evaluated thermochemical parameter values are proposed: GB(Arg)=1005+/-3 kJ.mol(-1); PA(Arg)=1051+/-5 kJ.mol(-1), and DeltapS degrees (Arg)=-45+/-12 J.mol(-1).K(-1)

Gas-Phase Lithium Cation Affinity of Glycine

International audienceThe gas-phase lithium cation binding thermochemistry of glycine has been determined theoretically by quantum chemical calculations at the G4 level and experimentally by the extended kinetic method using electrospray ionization quadrupole time-of-flight tandem mass spectrometry. The lithium cation affinity of glycine, ∆ Li H° 298 (GLY), i.e. the ∆ Li H° 298 of the reaction GlyLi + ® Gly + Li + , given by the G4 method is equal to 241.4 kJ mol-1 if only the most stable conformer of glycine is considered or to 242.3 kJ mol-1 if the 298 K equilibrium mixture of neutral conformers is included in the calculation. The ∆ Li H° 298 (GLY) deduced from the extended kinetic method is obviously dependent on the choice of the Li + affinity scale; thus, ∆ Li H° 298 (GLY) is equal to 228.7 ± 0.9(2.0) kJ mol-1 if anchored to the recently re-evaluated lithium cation affinity scale, but shifted to 235.4 ± 1.0 kJ mol-1 if G4 computed lithium cation affinities of the reference molecules are used. This difference of 6.3 kJ mol-1 may originate from a compression of the experimental lithium affinity scale in the high ∆ Li H° 298 region. The entropy change associated with the reaction GlyLi + ® Gly + Li + reveals a gain of approximately 15 J mol-1 K-1 with respect to monodentate Li + acceptors. The origin of this excess entropy is attributed to the bidentate interaction between the Li + cation and both the carbonyl oxygen and the nitrogen atoms of glycine. The computed G4 Gibbs free energy, ∆ Li G° 298 (GLY), is equal to 205.3 kJ mol-1 ; a similar result, 201.0 ± 3.4 kJ mol-1 , is obtained from the experiment if the ∆ Li G° 298 of the reference molecules is anchored on the G4 results

First Examples of Hybrids Based on Graphene and a Ring-Shaped Macrocyclic Polyoxometalate: Synthesis, Characterization, and Properties

This work introduces facile synthetic methods of two new classes of green materials based on graphene (G) and the macrocyclic polyoxometalate [H7P8W48O184]33 (P8W48) alone or assembled with an imidazolium-based poly(ionic liquid) (PIL). The polyoxometalate serves as both an efficient graphite oxide reductant and a stabilizer. Owing to the strong adsorption of P8W48 on the resulting G sheets, water-dispersible P8W48@G hybrids were obtained without the need for surfactant or polymeric stabilizers. The P8W48@G hybrids were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and cyclic voltammetry. The presence of G in these hybrids induces an outstanding enhancement in the electrochemical properties of P8W48 in comparison with those observed with glassy carbon. Moreover, P8W48@G- and P8W48@PIL-G-based electrodes exhibit remarkable stability during prolonged potential cycling in various aqueous electrolytes. To the best of our knowledge, these are the first examples of successful syntheses of a high nuclearity polyoxometalate and graphene assemblies that might facilitate photoelectrocatalysis of multielectronic reactions

Self-assembly of star-shaped heteropoly-15-palladate(II)

[EN] A novel heteropolyoxopalladate structural type has been discovered: the polyoxo-15-palladate(II) [Pd0.4Na0.6ÃPd15- P10O50H6.6] 12- (Pd15) has been prepared in a one-pot selfassembly reaction and characterized by single-crystal XRD, elemental analysis, IR, TGA, 31P NMR and electrochemistry; preliminary catalytic studies showed that Pd15 is active as a catalyst in alcohol oxidation by dioxygenU. K. thanks the German Science Foundation (DFG-KO-2288/9-1), the Fonds der Chemischen Industrie, and Jacobs University for research support. This work was also supported by the CNRS and the University Paris-Sud 11 (UMR 8000). Fig. 1-3 were generated by Diamond, Version 3.2 (copyright Crystal Impact GbR). We thank Dr. M. H. Dickman for help with XRD and L. Piedra-Garza for the registration of 31P NMR spectra.Izarova, NV.; Biboum, RN.; Keita, B.; Mifsud Grau, M.; Arends, IWCE.; Jameson, GB.; Kortz, U. (2009). Self-assembly of star-shaped heteropoly-15-palladate(II). Dalton Transactions. 43:9385-9387. https://doi.org/10.1039/b917079kS938593874