9 research outputs found
MolĂ©cules et matĂ©riaux Ă base de polyoxomĂ©tallates pour lâĂ©nergie et lâenvironnement
The present work concerns the synthesis and characterisation of new polyoxometalate (POMs) based molecules and materials for applications in energy and environment matters. As far as the environment is concerned, our efforts involved the electro-catalytic and photo-catalytic transformation of pollutants such as nitrogen oxides and recalcitrant azo dyes like Acid Orange 7. As for the domain of energy, we focused on electro-catalytic systems aimed at producing dihydrogen (a high calorific power fuel) and at reducing dioxygen (an important reagent in fuel cells). These reactions usually require several electrons in order to take place, which led us to choose POM-based catalysts. In fact, POMs are capable of stocking and returning an important number of electrons without changing their structure.In the first part, several POMs in which different transition metals are sandwiched in the equatorial plane of the molecular scaffold are synthesised and characterised by experimental (cyclic voltammetry, coulometry, microbalance) et theoretical (DFT calculations) methods. These compounds have shown a very good electro-catalytic activity towards the reduction of substrates such as nitrogen oxides, dioxygen and hydrogen peroxide.In the second part, some materials exhibiting improved properties are synthesised through the incorporation of POMs in matrices like Metal Organic Framework (MOF)-type molecular networks and ionic liquid polymers. The association with a semi-conductor such as TiOâ has also been considered. The materials obtained were characterised by several techniques: Fourier transform infrared spectroscopy, electrochemistry, diffuse reflectance spectroscopy, thermogravimetric analysis, X ray diffraction, X ray photoelectron spectroscopy, transmission electron microscopy. The POM and MOFs based materials are very performing for the electro-catalytic reduction of protons, having onset potentials better than those exhibited by platinum electrodes. The hybrids consisting of POMs, ionic liquid polymers and TiOâ are photo-sensitive under visible light, unlike each component taken individually. They have shown a good activity towards the degradation of Acid Orange 7. In addition, the composite obtained by photo-deposition of silver nanoparticles on these materials exhibits a good electro-catalytic performance as a cathode for the reduction of Oâ and NOâŸâ.Le prĂ©sent travail de thĂšse porte sur la synthĂšse et la caractĂ©risation de nouvelles molĂ©cules et matĂ©riaux Ă base de polyoxomĂ©tallates (POMs) pour des applications dans les domaines de lâĂ©nergie et lâenvironnement. Dans le domaine de lâenvironnement, notre choix sâest portĂ© sur la transformation Ă©lectro-catalytique et photo-catalytique des espĂšces polluantes comme les oxydes dâazote et les colorants azoĂŻques toxiques comme lâAcide Orange 7. Pour ce qui concerne le domaine de lâĂ©nergie, nous nous sommes focalisĂ©s sur des systĂšmes Ă©lectro- catalytiques pour la production de lâhydrogĂšne (combustible Ă fort pouvoir calorifique) et pour la rĂ©duction du di-oxygĂšne (intĂ©rĂȘt dans le fonctionnement des piles Ă combustibles). Ces rĂ©actions nĂ©cessitent gĂ©nĂ©ralement plusieurs Ă©lectrons pour se produire, câest pour cette raison que notre choix sâest portĂ© sur les catalyseurs Ă base de POMs. En effet, les POMs sont capables de stocker, puis de restituer, un grand nombre dâĂ©lectrons sans changer de structure.Dans la premiĂšre partie, divers POMs qui prennent en sandwich plusieurs mĂ©taux de transition sont synthĂ©tisĂ©s et caractĂ©risĂ©s par des mĂ©thodes expĂ©rimentales (voltamĂ©trie cyclique, coulomĂ©trie, microbalance) et thĂ©oriques (calculs DFT). Ces composĂ©s montrent une trĂšs bonne activitĂ© Ă©lectro-catalytique pour la rĂ©duction des substrats tels que les oxydes dâazote, le di-oxygĂšne et le peroxyde dâhydrogĂšne.Dans la seconde partie, des matĂ©riaux aux propriĂ©tĂ©s amĂ©liorĂ©es sont synthĂ©tisĂ©s par incorporation de POMs dans des matrices tels que les rĂ©seaux molĂ©culaires de type MOF (Metal Organic Framework) et dans les polymĂšres liquides ioniques. Lâassociation avec un semi-conducteur comme le TiOâ est aussi considĂ©rĂ©e. Les matĂ©riaux obtenus sont caractĂ©risĂ©s par diverses techniques : infrarouge Ă transformĂ©e de fourrier, Ă©lectrochimie, spectroscopie en rĂ©flectance diffuse, analyse thermogravimĂ©trique, diffraction de rayons X, spectroscopie de photo-Ă©lectrons X, microscopie Ă©lectronique Ă transmission. Les matĂ©riaux Ă base de POMs et de MOFs sont trĂšs performants pour la rĂ©duction Ă©lectro-catalytique des protons, avec des potentiels de dĂ©but effectif de la rĂ©action, meilleurs que ceux des Ă©lectrodes de platine. Les hybrides Ă base de POMs, de polymĂšres liquides ioniques et du TiOâ sont photo-sensibles sous lumiĂšre visible, contrairement Ă leurs composants. Ils dĂ©montrent une bonne activitĂ© vis-Ă -vis de la dĂ©gradation de lâAcide Orange 7. De plus, le composite obtenu par photo-dĂ©position de nanoparticules dâargent sur ces matĂ©riaux prĂ©sente de bonnes performances Ă©lectro-catalytiques comme cathode pour la rĂ©duction du Oâ et du NOâŸâ
New polyoxometalate based molecules and materials for applications in energy and environment matters
Le prĂ©sent travail de thĂšse porte sur la synthĂšse et la caractĂ©risation de nouvelles molĂ©cules et matĂ©riaux Ă base de polyoxomĂ©tallates (POMs) pour des applications dans les domaines de lâĂ©nergie et lâenvironnement. Dans le domaine de lâenvironnement, notre choix sâest portĂ© sur la transformation Ă©lectro-catalytique et photo-catalytique des espĂšces polluantes comme les oxydes dâazote et les colorants azoĂŻques toxiques comme lâAcide Orange 7. Pour ce qui concerne le domaine de lâĂ©nergie, nous nous sommes focalisĂ©s sur des systĂšmes Ă©lectro- catalytiques pour la production de lâhydrogĂšne (combustible Ă fort pouvoir calorifique) et pour la rĂ©duction du di-oxygĂšne (intĂ©rĂȘt dans le fonctionnement des piles Ă combustibles). Ces rĂ©actions nĂ©cessitent gĂ©nĂ©ralement plusieurs Ă©lectrons pour se produire, câest pour cette raison que notre choix sâest portĂ© sur les catalyseurs Ă base de POMs. En effet, les POMs sont capables de stocker, puis de restituer, un grand nombre dâĂ©lectrons sans changer de structure.Dans la premiĂšre partie, divers POMs qui prennent en sandwich plusieurs mĂ©taux de transition sont synthĂ©tisĂ©s et caractĂ©risĂ©s par des mĂ©thodes expĂ©rimentales (voltamĂ©trie cyclique, coulomĂ©trie, microbalance) et thĂ©oriques (calculs DFT). Ces composĂ©s montrent une trĂšs bonne activitĂ© Ă©lectro-catalytique pour la rĂ©duction des substrats tels que les oxydes dâazote, le di-oxygĂšne et le peroxyde dâhydrogĂšne.Dans la seconde partie, des matĂ©riaux aux propriĂ©tĂ©s amĂ©liorĂ©es sont synthĂ©tisĂ©s par incorporation de POMs dans des matrices tels que les rĂ©seaux molĂ©culaires de type MOF (Metal Organic Framework) et dans les polymĂšres liquides ioniques. Lâassociation avec un semi-conducteur comme le TiOâ est aussi considĂ©rĂ©e. Les matĂ©riaux obtenus sont caractĂ©risĂ©s par diverses techniques : infrarouge Ă transformĂ©e de fourrier, Ă©lectrochimie, spectroscopie en rĂ©flectance diffuse, analyse thermogravimĂ©trique, diffraction de rayons X, spectroscopie de photo-Ă©lectrons X, microscopie Ă©lectronique Ă transmission. Les matĂ©riaux Ă base de POMs et de MOFs sont trĂšs performants pour la rĂ©duction Ă©lectro-catalytique des protons, avec des potentiels de dĂ©but effectif de la rĂ©action, meilleurs que ceux des Ă©lectrodes de platine. Les hybrides Ă base de POMs, de polymĂšres liquides ioniques et du TiOâ sont photo-sensibles sous lumiĂšre visible, contrairement Ă leurs composants. Ils dĂ©montrent une bonne activitĂ© vis-Ă -vis de la dĂ©gradation de lâAcide Orange 7. De plus, le composite obtenu par photo-dĂ©position de nanoparticules dâargent sur ces matĂ©riaux prĂ©sente de bonnes performances Ă©lectro-catalytiques comme cathode pour la rĂ©duction du Oâ et du NOâŸâ.The present work concerns the synthesis and characterisation of new polyoxometalate (POMs) based molecules and materials for applications in energy and environment matters. As far as the environment is concerned, our efforts involved the electro-catalytic and photo-catalytic transformation of pollutants such as nitrogen oxides and recalcitrant azo dyes like Acid Orange 7. As for the domain of energy, we focused on electro-catalytic systems aimed at producing dihydrogen (a high calorific power fuel) and at reducing dioxygen (an important reagent in fuel cells). These reactions usually require several electrons in order to take place, which led us to choose POM-based catalysts. In fact, POMs are capable of stocking and returning an important number of electrons without changing their structure.In the first part, several POMs in which different transition metals are sandwiched in the equatorial plane of the molecular scaffold are synthesised and characterised by experimental (cyclic voltammetry, coulometry, microbalance) et theoretical (DFT calculations) methods. These compounds have shown a very good electro-catalytic activity towards the reduction of substrates such as nitrogen oxides, dioxygen and hydrogen peroxide.In the second part, some materials exhibiting improved properties are synthesised through the incorporation of POMs in matrices like Metal Organic Framework (MOF)-type molecular networks and ionic liquid polymers. The association with a semi-conductor such as TiOâ has also been considered. The materials obtained were characterised by several techniques: Fourier transform infrared spectroscopy, electrochemistry, diffuse reflectance spectroscopy, thermogravimetric analysis, X ray diffraction, X ray photoelectron spectroscopy, transmission electron microscopy. The POM and MOFs based materials are very performing for the electro-catalytic reduction of protons, having onset potentials better than those exhibited by platinum electrodes. The hybrids consisting of POMs, ionic liquid polymers and TiOâ are photo-sensitive under visible light, unlike each component taken individually. They have shown a good activity towards the degradation of Acid Orange 7. In addition, the composite obtained by photo-deposition of silver nanoparticles on these materials exhibits a good electro-catalytic performance as a cathode for the reduction of Oâ and NOâŸâ
Tuning the Dimensionality of Polyoxometalate-Based Materials by Using a Mixture of Ligands
Five molecular one-, two-, or three-dimensional
(1D, 2D, or 3D)
organicâinorganic hybrid polyoxometalates (POMs) based on the
{Δ-PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>ÂO<sub>40</sub>Zn<sub>4</sub>} (ΔZn) Keggin unit have been synthesized
under hydrothermal conditions using a mixture of O- and N-donor ligands.
(TBA)<sub>6</sub>Â[PMo<sup>V</sup><sub>8</sub>ÂMo<sup>VI</sup><sub>4</sub>O<sub>37</sub>Â(OH)<sub>3</sub>Zn<sub>4</sub>]<sub>2</sub>Â(C<sub>14</sub>H<sub>8</sub>O<sub>4</sub>)<sub>3</sub>·6H<sub>2</sub>O (<b>Δ</b><sub><b>2</b></sub><b>(biphen)</b><sub><b>3</b></sub>) is a 3D material
with two interpenetrated networks built from dimeric (ΔZn)<sub>2</sub> POMs linked by 4,4âČ-biphenyldicarboxylate (<b>biphen</b>) ligands. (TBA)<sub>2</sub>Â[PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>O<sub>38</sub>Â(OH)<sub>2</sub>Zn<sub>4</sub>]Â(C<sub>7</sub>H<sub>6</sub>N<sub>2</sub>)<sub>3</sub>Â(C<sub>14</sub>H<sub>8</sub>O<sub>4</sub>)<sub>1/2</sub>·H<sub>2</sub>O (<b>ΔÂ(bim)</b><sub><b>3</b></sub><b>(biphen)</b><sub><b>1/2</b></sub>), (TBA)<sub>3</sub>Â[PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>O<sub>38</sub>Â(OH)<sub>2</sub>Zn<sub>4</sub>]Â(C<sub>7</sub>H<sub>6</sub>N<sub>2</sub>)<sub>2</sub>Â(C<sub>8</sub>H<sub>4</sub>O<sub>4</sub>)·6H<sub>2</sub>O (<b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(isop)</b>), (TBA)<sub>7/3</sub>Â[PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>O<sub>38</sub>Â(OH)<sub>2</sub>Zn<sub>4</sub>]Â(C<sub>7</sub>H<sub>6</sub>N<sub>2</sub>)<sub>8/3</sub>Â(C<sub>8</sub>H<sub>4</sub>O<sub>4</sub>)<sub>2/3</sub> (<b>ΔÂ(bim)</b><sub><b>8/3</b></sub><b>(bdc)</b><sub><b>2/3</b></sub>), and (TBA)<sub>3</sub>Â[PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>O<sub>38</sub>(OH)<sub>2</sub>Zn<sub>4</sub>]Â(C<sub>7</sub>H<sub>6</sub>N<sub>2</sub>)<sub>2</sub>Â(C<sub>9</sub>H<sub>3</sub>O<sub>6</sub>)<sub>2/3</sub>·6H<sub>2</sub>O (<b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(trim)</b><sub><b>2/3</b></sub>) all
consist of monomeric ΔZn units bound to two types of organic
ligands: benzimidazole (<b>bim</b>) and one of the following
carboxylate ligands: <b>biphen</b>, 1,3-benzenedicarboxylate
(<b>isop</b>), 1,4-benzenedicarboxylate (<b>bdc</b>),
or 1,3,5-benzenetricarboxylate (<b>trim</b>) ligands. While <b>ΔÂ(bim)</b><sub><b>3</b></sub><b>(biphen)</b><sub><b>1/2</b></sub> is a molecular complex, <b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(isop)</b> and <b>ΔÂ(bim)</b><sub><b>8/3</b></sub><b>(bdc)</b><sub><b>2/3</b></sub> adopt a chain arrangement, and <b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(trim)</b><sub><b>2/3</b></sub> is a 2D compound. In these materials, the limitation of the dimensionality
is a direct consequence of the protonation of the nitrogen atom of
the <b>bim</b> ligands. The electrocatalytic activity for the
hydrogen evolution reaction (HER) of these five new POM-based coordination
polymers has been studied, showing that their performance depends
mainly on the presence of the ΔZn Keggin units but also on their
structure. Modified electrodes fabricated with <b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(trim)</b><sub><b>2/3</b></sub> entrapped in a carbon paste revealed that this hybrid is the
most efficient electrocatalyst of the series, being stable and catalyzing
the HER in the pH 1â5 range
Tuning the Dimensionality of Polyoxometalate-Based Materials by Using a Mixture of Ligands
Five molecular one-, two-, or three-dimensional
(1D, 2D, or 3D)
organicâinorganic hybrid polyoxometalates (POMs) based on the
{Δ-PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>ÂO<sub>40</sub>Zn<sub>4</sub>} (ΔZn) Keggin unit have been synthesized
under hydrothermal conditions using a mixture of O- and N-donor ligands.
(TBA)<sub>6</sub>Â[PMo<sup>V</sup><sub>8</sub>ÂMo<sup>VI</sup><sub>4</sub>O<sub>37</sub>Â(OH)<sub>3</sub>Zn<sub>4</sub>]<sub>2</sub>Â(C<sub>14</sub>H<sub>8</sub>O<sub>4</sub>)<sub>3</sub>·6H<sub>2</sub>O (<b>Δ</b><sub><b>2</b></sub><b>(biphen)</b><sub><b>3</b></sub>) is a 3D material
with two interpenetrated networks built from dimeric (ΔZn)<sub>2</sub> POMs linked by 4,4âČ-biphenyldicarboxylate (<b>biphen</b>) ligands. (TBA)<sub>2</sub>Â[PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>O<sub>38</sub>Â(OH)<sub>2</sub>Zn<sub>4</sub>]Â(C<sub>7</sub>H<sub>6</sub>N<sub>2</sub>)<sub>3</sub>Â(C<sub>14</sub>H<sub>8</sub>O<sub>4</sub>)<sub>1/2</sub>·H<sub>2</sub>O (<b>ΔÂ(bim)</b><sub><b>3</b></sub><b>(biphen)</b><sub><b>1/2</b></sub>), (TBA)<sub>3</sub>Â[PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>O<sub>38</sub>Â(OH)<sub>2</sub>Zn<sub>4</sub>]Â(C<sub>7</sub>H<sub>6</sub>N<sub>2</sub>)<sub>2</sub>Â(C<sub>8</sub>H<sub>4</sub>O<sub>4</sub>)·6H<sub>2</sub>O (<b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(isop)</b>), (TBA)<sub>7/3</sub>Â[PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>O<sub>38</sub>Â(OH)<sub>2</sub>Zn<sub>4</sub>]Â(C<sub>7</sub>H<sub>6</sub>N<sub>2</sub>)<sub>8/3</sub>Â(C<sub>8</sub>H<sub>4</sub>O<sub>4</sub>)<sub>2/3</sub> (<b>ΔÂ(bim)</b><sub><b>8/3</b></sub><b>(bdc)</b><sub><b>2/3</b></sub>), and (TBA)<sub>3</sub>Â[PMo<sup>V</sup><sub>8</sub>Mo<sup>VI</sup><sub>4</sub>O<sub>38</sub>(OH)<sub>2</sub>Zn<sub>4</sub>]Â(C<sub>7</sub>H<sub>6</sub>N<sub>2</sub>)<sub>2</sub>Â(C<sub>9</sub>H<sub>3</sub>O<sub>6</sub>)<sub>2/3</sub>·6H<sub>2</sub>O (<b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(trim)</b><sub><b>2/3</b></sub>) all
consist of monomeric ΔZn units bound to two types of organic
ligands: benzimidazole (<b>bim</b>) and one of the following
carboxylate ligands: <b>biphen</b>, 1,3-benzenedicarboxylate
(<b>isop</b>), 1,4-benzenedicarboxylate (<b>bdc</b>),
or 1,3,5-benzenetricarboxylate (<b>trim</b>) ligands. While <b>ΔÂ(bim)</b><sub><b>3</b></sub><b>(biphen)</b><sub><b>1/2</b></sub> is a molecular complex, <b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(isop)</b> and <b>ΔÂ(bim)</b><sub><b>8/3</b></sub><b>(bdc)</b><sub><b>2/3</b></sub> adopt a chain arrangement, and <b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(trim)</b><sub><b>2/3</b></sub> is a 2D compound. In these materials, the limitation of the dimensionality
is a direct consequence of the protonation of the nitrogen atom of
the <b>bim</b> ligands. The electrocatalytic activity for the
hydrogen evolution reaction (HER) of these five new POM-based coordination
polymers has been studied, showing that their performance depends
mainly on the presence of the ΔZn Keggin units but also on their
structure. Modified electrodes fabricated with <b>ΔÂ(bim)</b><sub><b>2</b></sub><b>(trim)</b><sub><b>2/3</b></sub> entrapped in a carbon paste revealed that this hybrid is the
most efficient electrocatalyst of the series, being stable and catalyzing
the HER in the pH 1â5 range
Tetradecanuclear iron(III)-oxo nanoclusters stabilized by trilacunary heteropolyanions
The
tetrameric, multi-Fe<sup>III</sup>-containing polyoxotungstates
[Fe<sub>14</sub>O<sub>6</sub>(OH)<sub>13</sub>Â(P<sub>2</sub>W<sub>15</sub>O<sub>56</sub>)<sub>4</sub>]<sup>31â</sup> (<b>1</b>) and [Na<sub>2</sub>Fe<sub>14</sub>(OH)<sub>12</sub>Â(PO<sub>4</sub>)<sub>4</sub>(<i>A</i>-α-XW<sub>9</sub>O<sub>34</sub>)<sub>4</sub>]<sup>20â</sup> (X = Si<sup>IV</sup> (<b>2</b>), Ge<sup>IV</sup> (<b>3</b>)) have been successfully
synthesized under conventional reaction conditions in aqueous, slightly
acidic (<b>1</b>), or basic (<b>2</b> and <b>3</b>) media. Polyanions <b>1-3</b> were characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and magnetic studies, and in solution by electrochemistry