Immobilisation de Polyoxométallates dans des Metal-Organic Frameworks pour la Photocatalyse Hétérogène

New PolyOxoMetalate-based (POM) hybrid materials were synthetized by impregnating POMs inside the porous cavities of MOF-545 (Metal-Organic Frameworks) in aqueous media. POMs were selected based on their catalytic properties toward water oxidation or proton reduction. The obtained ‘POM@MOF-545’ were then fully characterized by an array of physical and chemical methods (RMN and X-ray absorption spectroscopy, DRX) to prove both the stability of POM and MOF in the obtained composite. In particular, the P2W18Co4@MOF-545 showed a catalytic toward water oxydation to oxygen without the need for an external photosensitizer other than the MOF-545 itself. Thus, it is a multifunctional, noble-metal free hybrid for photo-catalysis. Then, P2W18Co4@MOF-545 was studied as thin-films deposited on ITO electrode. Two pathways for electrodes realization were studied : drop-casting and electro-phoretic deposition. The electro- and photo-catalytic activities of both deposition were compared. Finally, a new POM, SiW9Ni14Ale7 were studied for photo-reduction of proton into hydrogen using an iridium complex as photosensitizer. Photo-physical measurements proved that the reaction mechanism was following an oxidative quenching pathway.De nouveaux matériaux hybrides à base de polyoxométallates (POMs) incorporer dans les cavités poreuses du MOF-545 (Metal-Organic Framework) ont été synthétisés par la méthode douce d'imprégnation en milieu aqueux. Les POMs ont été choisis pour leurs propriétés catalytiques envers l'oxydation de l'eau ou la réduction du proton. Ces "POM@MOF-545" ont ensuite été caractérisés par des méthodes physico-chimiques (spectroscopie RMN, d'absorption X, DRX) afin de montrer la stabilité à la fois du POM et du MOF dans le composite obtenu. En particulier, le P2W18Co4@MOF-545 a montré une activité catalytique pour la photo-oxydation de l'eau en dioxygène sans ajout de photo-sensibilisateurs supplémentaires. Il s’agit donc d’une plateforme multifonctionnelle, sans métaux nobles, pour la photo-catalyse. Dans un deuxième temps ce P2W18Co4@MOF-545 a été étudié sous forme de couche-mince à la surface d’électrode d’ITO. Ces électrodes ont été réalisées de deux façons, par drop-casting et par dépôt électro-phorétique. Les activités électro- et photo- catalytiques pour l’oxydation de l’eau de ces deux couches-minces ont été comparées. Un nouveau POM, le SiW9Ni14Ale7 a également été étudié pour la photo-réduction du proton en dihydrogène en utilisant un complexe d’iridium comme photo-sensibilisateur. Des mesures photo-physiques ont révélé un mécanisme de type quenching oxydant

Immobilisation de Polyoxométallates dans des Metal-Organic Frameworks pour la Photocatalyse Hétérogène

New PolyOxoMetalate-based (POM) hybrid materials were synthetized by impregnating POMs inside the porous cavities of MOF-545 (Metal-Organic Frameworks) in aqueous media. POMs were selected based on their catalytic properties toward water oxidation or proton reduction. The obtained ‘POM@MOF-545’ were then fully characterized by an array of physical and chemical methods (RMN and X-ray absorption spectroscopy, DRX) to prove both the stability of POM and MOF in the obtained composite. In particular, the P2W18Co4@MOF-545 showed a catalytic toward water oxydation to oxygen without the need for an external photosensitizer other than the MOF-545 itself. Thus, it is a multifunctional, noble-metal free hybrid for photo-catalysis. Then, P2W18Co4@MOF-545 was studied as thin-films deposited on ITO electrode. Two pathways for electrodes realization were studied : drop-casting and electro-phoretic deposition. The electro- and photo-catalytic activities of both deposition were compared. Finally, a new POM, SiW9Ni14Ale7 were studied for photo-reduction of proton into hydrogen using an iridium complex as photosensitizer. Photo-physical measurements proved that the reaction mechanism was following an oxidative quenching pathway.De nouveaux matériaux hybrides à base de polyoxométallates (POMs) incorporer dans les cavités poreuses du MOF-545 (Metal-Organic Framework) ont été synthétisés par la méthode douce d'imprégnation en milieu aqueux. Les POMs ont été choisis pour leurs propriétés catalytiques envers l'oxydation de l'eau ou la réduction du proton. Ces "POM@MOF-545" ont ensuite été caractérisés par des méthodes physico-chimiques (spectroscopie RMN, d'absorption X, DRX) afin de montrer la stabilité à la fois du POM et du MOF dans le composite obtenu. En particulier, le P2W18Co4@MOF-545 a montré une activité catalytique pour la photo-oxydation de l'eau en dioxygène sans ajout de photo-sensibilisateurs supplémentaires. Il s’agit donc d’une plateforme multifonctionnelle, sans métaux nobles, pour la photo-catalyse. Dans un deuxième temps ce P2W18Co4@MOF-545 a été étudié sous forme de couche-mince à la surface d’électrode d’ITO. Ces électrodes ont été réalisées de deux façons, par drop-casting et par dépôt électro-phorétique. Les activités électro- et photo- catalytiques pour l’oxydation de l’eau de ces deux couches-minces ont été comparées. Un nouveau POM, le SiW9Ni14Ale7 a également été étudié pour la photo-réduction du proton en dihydrogène en utilisant un complexe d’iridium comme photo-sensibilisateur. Des mesures photo-physiques ont révélé un mécanisme de type quenching oxydant

A Multifunctional Dual-Luminescent Polyoxometalate@Metal-Organic Framework EuW10@UiO-67 Composite as Chemical Probe and Temperature Sensor

International audienceThe luminescent [EuW10O36]9− polyoxometalate has been introduced into the cavities of the highly porous zirconium luminescent metal-organic framework UiO-67 via a direct synthesis approach, affording the EuW10@UiO-67 hybrid. Using a combination of techniques (TGA, BET, elemental analysis, EDX mapping,…) this new material has been fully characterized, evidencing that it contains only 0.25% in europium and thatthe polyoxometalate units are located inside the octahedral cavities and not at the surface of the UiO-67 crystallites. Despite the low amount of europium, it is shown that EuW10@UiO-67 acts as a solid-state luminescent sensor for the detection of amino-acids, the growth of the emission intensity globally following the growth of the amino-acid pKa. In addition, EuW10@UiO-67 acts as a sensor for the detection ofmetalliccations, with a high sensitivity for Fe3+. Noticeably, the recyclability of the reported material has been established. Finally, it is shown that the dual-luminescent EuW10@UiO-67 material behave as a self-calibrated-ratiometric thermometer in the physiological range

A Fully Noble Metal-Free Photosystem Based on Cobalt- Polyoxometalates Immobilized in a Porphyrinic Metal- Organic-Framework for Water Oxidation

International audienceThe sandwich-type polyoxometalate (POM) [(PW 9 O 34) 2 Co 4 (H 2 O) 2 ] 10-was immobilized in the hexagonal channels of the Zr(IV) porphyrinic MOF-545 hybrid framework. The resulting composite was fully characterized by a panel of physicochemical techniques. Calculations allowed identifying the localization of the POM in the vicinity of the Zr 6 clusters and porphyrin linkers constituting the MOF. The material exhibits a high photocatalytic activity and good stability for visible-light-driven water oxidation. It thus represents a rare example of an all-in-one fully noble metal-free supramolecular heterogeneous photocatalytic system, with the catalyst and the photosensitizer within the same porous solid material

Effect of Cations on the Structure and Electrocatalytic Response of Polyoxometalate-Based Coordination Polymers

International audienceA series of six hybrid polymers based on the mixed-valent {ε-PMoV8MoVI4O40Zn4} (εZn) Keggin unit have been synthesized under hydrothermal conditions using tritopic (1,3,5-benzenetricarboxylate (trim) or 1,3,5-benzenetribenzoate (BTB)) or ditopic (4,4′-biphenyldicarboxylate (biphen)) linkers and [M(bpy)3]2+ (M = Co, Ru) complexes as charge-compensating cations. (TBA)2[Co(C10H8N2)3][PMo12O37(OH)3Zn4](C27H15O6)4/3·1.5C27H18O6·24H2O (Co-ε(BTB)4/3) has a three-dimensional (3D) framework with two interpenetrated networks and is isostructural to (TBA)4[PMo12O37(OH)3Zn4](C27H15O6)4/3·1.5C27H18O6·8H2O (ε(BTB)4/3). In Co-ε(BTB)4/3, two tetrabutylammonium (TBA+) cations over the four present in ε(BTB)4/3 are replaced by one [Co(bpy)3]2+ complex. [Co(C10H8N2)3][PMo12O37(OH)3Zn4](C9H3O6)Co(C10H8N2)4(H2O)·16H2O (Co-ε(trim) (bpy)2) is a 1D coordination polymer with two types of CoII-containing complexes, one covalently attached to the 1D chains and the other located in the voids as the counterion. [Ru(C10H8N2)3]4[PMo12O38(OH)2Zn4]2(C9H3O6)2·42H2O (Ru-ε2(trim)2) and [Ru(C10H8N2)3]3[PMo12O37(OH)3Zn4Cl]2(C14H8O4)2·24H2O (Ru-ε2(biphen)2) contain dimeric (εZn)2 units linked by dicarboxylate linkers, and both have [Ru(bpy)3]2+ countercations. Ru-ε2(trim)2 has a 3D framework, while Ru-ε2(biphen)2 is only 2D because of the presence of chloride ions on one-fourth of the ZnII ions. [P(C6H5)4]6[PMo12O37(OH)3Zn4]2(C9H3O6)2·18H2O (PPh4-ε2(trim)2) is isostructural to Ru-ε2(trim)2. These insoluble compounds entrapped in carbon-paste electrodes exhibit electrocatalytic activity for the hydrogen evolution reaction. The effects of their structure and the nature of the counterions on the activity have been studied. For the first time, different POM-based coordination polymers are compared for catalytic H2 production using controlled-potential electrolysis. This study shows that the nature of the countercation has a strong effect on the electrocatalytic activity of the compound

Thin Films of Fully Noble Metal-Free POM@MOF for Photocatalytic Water Oxidation

International audienceP2 W18Co 4@MOF-545 which contains the sandwich-type polyoxometalate (POM) [(PW 9 O 34) 2 Co 4 (H 2 O) 2 ] 10-(P 2 W 18 Co 4) immobilized in the porphyrinic MOF-545 framework, is a "three-in-one" (porosity + light capture + catalysis) heterogeneous photosystem for the oxygen evolution reaction (OER). Thin films of this composite were synthesized on transparent and conductive indium tin oxide (ITO) supports using electrophoretic (EP) or drop casting (DC) methods, thus providing easy-to-use devices. Their electro-and photocatalytic activities for OER were investigated. Remarkably, both types of films exhibit higher turnover numbers (TONs) than the original bulk material previously studied as suspension for the photocatalytic OER, with TONs after 2 hours equal to 1600 and 403 for DC and EP films respectively compared to 70 for the suspension. This difference of catalytic activities is related to the proportion of efficiently illuminated crystallites, whereby a DC thin film offers the largest proportion of POM@MOF crystallites exposed to light due to its lower thickness when compared to an EP film or crystals in suspension. Such devices can be easily recycled by simply removing them from the reaction medium and washing them before reuse. The films were fully characterized with EXAFS and XANES spectroscopies, Raman, Scanning Electron Microscopy and electrochemistry, before and after catalysis. The combination of all these techniques shows the stability of both the POM and the MOF within the composite upon water oxidation reaction

Interfacing MOFs with active components for the development of hybrid porous materials.

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An unprecedented {Ni 14 SiW 9 } hybrid polyoxometalate with high photocatalytic hydrogen evolution activity

International audienceA unique polyoxometalate complex made up of a tetradecanuclear nickel bisphosphonate cluster capping a {SiW9} unit has been characterized. This stable compound exhibits a high hydrogen evolution reaction photocatalytic activity under visible light irradiation via a reductive quenching mechanism